Targeting cancer metabolism to develop human lactate dehydrogenase ( h LDH)5 inhibitors

The interplay between the tumor microenvironment and tumor-derived small extracellular vesicles in cancer development and therapeutic response

The tumor microenvironment (TME) plays an essential role in tumor cell survival by profoundly influencing their proliferation, metastasis, immune evasion, and resistance to treatment. Extracellular vesicles (EVs) are small particles released by all cell types and often reflect the state of their parental cells and modulate other cells' functions through the various cargo they transport. Tumor-derived small EVs (TDSEVs) can transport specific proteins, nucleic acids and lipids tailored to propagate tumor signals and establish a favorable TME. Thus, the TME's biological characteristics can affect TDSEV heterogeneity, and this interplay can amplify tumor growth, dissemination, and resistance to therapy. This review discusses the interplay between TME and TDSEVs based on their biological characteristics and summarizes strategies for targeting cancer cells. Additionally, it reviews the current issues and challenges in this field to offer fresh insights into comprehending tumor development mechanisms and exploring innovative clinical applications.

Novel indole Schiff base β-diiminato compound as an anti-cancer agent against triple-negative breast cancer: In vitro anticancer activity evaluation and in vivo acute toxicity study

Breast cancer is the most prevalent cancer among women globally, with triple-negative breast cancer (TNBC) associated with poor prognosis and low five-year survival rates. Schiff base compounds, known for their extensive pharmacological activities, have garnered significant attention in cancer drug research. This study aimed to evaluate the anticancer potential of a novel β-diiminato compound and elucidate its mechanism of action. The compound's effect on cell viability was assessed using MTT assays in breast cancer cell lines including MCF-7 and MDA-MB-231. Cytotoxic effects were further analyzed using trypan blue exclusion and lactate dehydrogenase (LDH) release assays. In order to assess the mechanism of inhibitory activity and mode of cell death induced by this compound, flow cytometry of cell cycle distribution and apoptosis analysis were carried out. Apoptosis incidence was initially assessed through cell and nuclear morphological changes (Hoechst 33342/Propidium iodide (PI) staining) and further confirmed by Annexin V/PI staining and flow cytometry analysis. In addition, the effect of this compound on the disruption of mitochondrial membrane potential (MMP) and generation of the reactive oxygen species (ROS) was determined using the JC-1 indicator and DCFDA dye, respectively. The results demonstrated that the 24 h treatment with β-diiminato compound significantly suppressed the viability of MDA-MB-231 and MCF-7 cancer cells in a dose-dependent manner with the IC50 value of 2.41 ± 0.29 and 3.51 ± 0.14, respectively. The cytotoxic effect of the compound was further confirmed with a dose-dependent increase in the number of dead cells and enhanced LDH level in the culture medium. This compound exerted its anti-proliferative effect by G2/M phase cell growth arrest in MDA-MB-231 breast cancer cells and induced apoptosis-mediated cell death, which involved characteristic changes in cell and nuclear morphology, phosphatidylserine externalization, mitochondrial membrane depolarization, and increased ROS level. Neither hepatotoxicity nor nephrotoxicity was detected in the biochemical and histopathological analysis confirming the safety characterization of this compound usage. Therefore, the results significantly confirmed the potential anticancer activity of a novel β-diiminato compound, as evidenced by the induction of cell cycle arrest and apoptosis, which might be driven by the ROS‑mediated mitochondrial death pathway. This compound can be a promising candidate for future anticancer drug design and TNBC treatment, and further preclinical and clinical studies are warranted.

Development of human lactate dehydrogenase a inhibitors: high-throughput screening, molecular dynamics simulation and enzyme activity assay

Lactate dehydrogenase A (LDHA) is highly expressed in many tumor cells and promotes the conversion of pyruvate to lactic acid in the glucose pathway, providing energy and synthetic precursors for rapid proliferation of tumor cells. Therefore, inhibition of LDHA has become a widely concerned tumor treatment strategy. However, the research and development of highly efficient and low toxic LDHA small molecule inhibitors still faces challenges. To discover potential inhibitors against LDHA, virtual screening based on molecular docking techniques was performed from Specs database of more than 260,000 compounds and Chemdiv-smart database of more than 1,000 compounds. Through molecular dynamics (MD) simulation studies, we identified 12 potential LDHA inhibitors, all of which can stably bind to human LDHA protein and form multiple interactions with its active central residues. In order to verify the inhibitory activities of these compounds, we established an enzyme activity assay system and measured their inhibitory effects on recombinant human LDHA. The results showed that Compound 6 could inhibit the catalytic effect of LDHA on pyruvate in a dose-dependent manner with an EC50 value of 14.54 ± 0.83 µM. Further in vitro experiments showed that Compound 6 could significantly inhibit the proliferation of various tumor cell lines such as pancreatic cancer cells and lung cancer cells, reduce intracellular lactic acid content and increase intracellular reactive oxygen species (ROS) level. In summary, through virtual screening and in vitro validation, we found that Compound 6 is a small molecule inhibitor for LDHA, providing a good lead compound for the research and development of LDHA related targeted anti-tumor drugs.

Inhibition of lactate dehydrogenase A by diclofenac sodium induces apoptosis in HeLa cells through activation of AMPK

Cancer cells exhibit a unique metabolic preference for the glycolytic pathway over oxidative phosphorylation for maintaining the tumor microenvironment. Lactate dehydrogenase A (LDHA) is a key enzyme that facilitates glycolysis by converting pyruvate to lactate and has been shown to be upregulated in multiple cancers due to the hypoxic tumor microenvironment. Diclofenac (DCF), a nonsteroidal anti-inflammatory drug, has been shown to exhibit anticancer effects by interfering with the glucose metabolism pathway. However, the specific targets of this drug remain unknown. Using in silico, biochemical, and biophysical studies, we show that DCF binds to LDHA adjacent to the substrate binding site and inhibits its activity in a dose-dependent and allosteric manner in HeLa cells. Thus, DCF inhibits the hypoxic microenvironment and induces apoptosis-mediated cell death. DCF failed to induce cytotoxicity in HeLa cells when LDHA was knocked down, confirming that DCF exerts its antimitotic effects via LDHA inhibition. DCF-induced LDHA inhibition alters pyruvate, lactate, NAD+, and ATP production in cells, and this could be a possible mechanism through which DCF inhibits glucose uptake in cancer cells. DCF-induced ATP deprivation leads to mitochondria-mediated oxidative stress, which results in DNA damage, lipid peroxidation, and apoptosis-mediated cell death. Reduction in intracellular ATP levels additionally activates the sensor kinase, adenosine monophosphate-activated protein kinase (AMPK), which further downregulates phosphorylated ribosomal S6 kinase (p-S6K), leading to apoptosis-mediated cell death. We find that in LDHA knocked down cells, intracellular ATP levels were depleted, resulting in the inhibition of p-S6K, suggesting the involvement of DCF-induced LDHA inhibition in the activation of the AMPK/S6K signaling pathway.

Metabolic Rewiring in Cancer: Small Molecule Inhibitors in Colorectal Cancer Therapy

Alterations in cellular metabolism, such as dysregulation in glycolysis, lipid metabolism, and glutaminolysis in response to hypoxic and low-nutrient conditions within the tumor microenvironment, are well-recognized hallmarks of cancer. Therefore, understanding the interplay between aerobic glycolysis, lipid metabolism, and glutaminolysis is crucial for developing effective metabolism-based therapies for cancer, particularly in the context of colorectal cancer (CRC). In this regard, the present review explores the complex field of metabolic reprogramming in tumorigenesis and progression, providing insights into the current landscape of small molecule inhibitors targeting tumorigenic metabolic pathways and their implications for CRC treatment.

Combined inhibition of pyruvate dehydrogenase kinase 1 and lactate dehydrogenase a induces metabolic and signaling reprogramming and enhances lung adenocarcinoma cell killing

Lung adenocarcinoma (LUAD) is one of the most prevalent and aggressive types of lung cancer. Metabolic reprogramming plays a critical role in the development and progression of LUAD. Pyruvate dehydrogenase kinase 1 (PDK1) and lactate dehydrogenase A (LDHA) are two key enzymes involved in glucose metabolism, whilst their aberrant expressions are often associated with tumorigenesis. Herein, we investigated the anticancer effects of combined inhibition of PDK1 and LDHA in LUAD in vitro and in vivo and its underlying mechanisms of action. The combination of a PDK1 inhibitor, 64, and a LDHA inhibitor, NHI-Glc-2, led to a synergistic growth inhibition in 3 different LUAD cell lines and more than additively suppressed tumor growth in the LUAD xenograft H1975 model. This combination also inhibited cellular migration and colony formation, while it induced a metabolic shift from glycolysis to oxidative phosphorylation (OXPHOS) resulting in mitochondrial depolarization and apoptosis in LUAD cells. These effects were related to modulation of multiple cell signaling pathways, including AMPK, RAS/ERK, and AKT/mTOR. Our findings demonstrate that simultaneous inhibition of multiple glycolytic enzymes (PDK1 and LDHA) is a promising novel therapeutic approach for LUAD.

Preparation of a Mesoporous Biosensor for Human Lactate Dehydrogenase for Potential Anticancer Inhibitor Screening

Cancer is the second leading cause of death worldwide, with a dramatic impact due to the acquired resistance of cancers to used chemotherapeutic drugs and treatments. The enzyme lactate dehydrogenase (LDH-A) is responsible for cancer cell proliferation. Recently the development of selective LDH-A inhibitors as drugs for cancer treatment has been reported to be an efficient strategy aiming to decrease cancer cell proliferation and increase the sensitivity to traditional chemotherapeutics. This study aims to obtain a stable and active biocatalyst that can be utilized for such drug screening purposes. It is conceived by adopting human LDH-A enzyme (hLDH-A) and investigating different immobilization techniques on porous supports to achieve a stable and reproducible biosensor for anticancer drugs. The hLDH-A enzyme is covalently immobilized on mesoporous silica (MCM-41) functionalized with amino and aldehyde groups following two different methods. The mesoporous support is characterized by complementary techniques to evaluate the surface chemistry and the porous structure. Fluorescence microscopy analysis confirms the presence of the enzyme on the support surface. The tested immobilizations achieve yields of ≥80%, and the best retained activity of the enzyme is as high as 24.2%. The optimal pH and temperature of the best immobilized hLDH-A are pH 5 and 45 °C for the reduction of pyruvate into lactate, while those for the free enzyme are pH 8 and 45 °C. The stability test carried out at 45 °C on the immobilized enzyme shows a residual activity close to 40% for an extended time. The inhibition caused by NHI-2 is similar for free and immobilized hLDH-A, 48% and 47%, respectively. These findings are significant for those interested in immobilizing enzymes through covalent attachment on inorganic porous supports and pave the way to develop stable and active biocatalyst-based sensors for drug screenings that are useful to propose drug-based cancer treatments.

Reprogramming Energy Metabolism with Synthesized PDK Inhibitors Based on Dichloroacetate Derivatives and Targeted Delivery Systems for Enhanced Cancer Therapy

In many types of cancers, pyruvate dehydrogenase kinase (PDK) is abnormally overexpressed and has become a promising target for cancer therapy. However, few highly effective inhibitors of PDK have been reported to date. Herein, we designed and synthesized a series of PDK inhibitors based on dichloroacetate (DCA) and arsenicals. Of the 27 compounds, 1f demonstrated PDK inhibition with high efficiency at a cellular level (IC50 = 2.0 μM) and an enzyme level (EC50 = 68 nM), far more effective than that of DCA. In silico, in vitro, and in vivo studies demonstrated that 1f inhibited PDK, shifted the energy metabolism from aerobic glycolysis to oxidative phosphorylation, and induced cell apoptosis. Moreover, new 1f-loaded nanoparticles were developed, and the administration of high-drug-loading nanoparticles (0.15 mg/kg) caused up to 90% tumor shrinkage without any apparent toxicity. Hence, this study provided a novel metabolic therapy for cancer treatment.

Potential targeting of the tumor microenvironment to improve cancer virotherapy

In 2015, oncolytic virotherapy was approved for clinical use, and in 2017, recombinant adeno-associated virus (AAV) delivery was also approved. However, systemic administration remains challenging due to the limited number of viruses that successfully reach the target site. Although the US Food and Drug Administration (FDA) permits the use of higher doses of AAV to achieve greater rates of transduction, most AAV still accumulates in the liver, potentially leading to toxicity there and elsewhere. Targeting the tumor microenvironment is a promising strategy for cancer treatment due to the critical role of the tumor microenvironment in controlling tumor progression and influencing the response to therapies. Newly discovered evidence indicates that administration routes focusing on the tumor microenvironment can promote delivery specificity and transduction efficacy within the tumor. Here, we review approaches that involve modifying viral surface features, modulating the immune system, and targeting the physicochemical characteristics in tumor microenvironment to regulate therapeutic delivery. Targeting tumor acidosis presents advantages that can be leveraged to enhance virotherapy outcomes and to develop new therapeutic approaches that can be integrated with standard treatments.

Synthesis and hLDH Inhibitory Activity of Analogues to Natural Products with 2,8-Dioxabicyclo[3.3.1]nonane Scaffold

Human lactate dehydrogenase (hLDH) is a tetrameric enzyme present in almost all tissues. Among its five different isoforms, hLDHA and hLDHB are the predominant ones. In the last few years, hLDHA has emerged as a therapeutic target for the treatment of several kinds of disorders, including cancer and primary hyperoxaluria. hLDHA inhibition has been clinically validated as a safe therapeutic method and clinical trials using biotechnological approaches are currently being evaluated. Despite the well-known advantages of pharmacological treatments based on small-molecule drugs, few compounds are currently in preclinical stage. We have recently reported the detection of some 2,8-dioxabicyclo[3.3.1]nonane core derivatives as new hLDHA inhibitors. Here, we extended our work synthesizing a large number of derivatives (42-70) by reaction between flavylium salts (27-35) and several nucleophiles (36-41). Nine 2,8-dioxabicyclo[3.3.1]nonane derivatives showed IC₅₀ values lower than 10 µM against hLDHA and better activity than our previously reported compound 2. In order to know the selectivity of the synthesized compounds against hLDHA, their hLDHB inhibitory activities were also measured. In particular, compounds 58, 62a, 65b, and 68a have shown the lowest IC₅₀ values against hLDHA (3.6-12.0 µM) and the highest selectivity rate (>25). Structure-activity relationships have been deduced. Kinetic studies using a Lineweaver-Burk double-reciprocal plot have indicated that both enantiomers of 68a and 68b behave as noncompetitive inhibitors on hLDHA enzyme.

Ent-kaurenoic acid-enriched Mikania glomerata leaves-complexed β-cyclodextrin: Pharmaceutical development and in vivo antitumor activity in a sarcoma 180 mouse model

The extract obtained from Mikania glomerata leaves rich in ent-kaurenoic acid (ERKA) shows cytotoxic activity in vitro, but its hydrophobic nature and thermosensitivity are issues to be solved prior to in vivo antitumor studies. The purpose of this study was to investigate the antitumor activity of inclusion complexes formed between ERKA and β-cyclodextrin (ERKA:β-CD) in rodents. ERKA:β-CD complexes obtained by malaxation (MX) and co-evaporation (CE) methods were firstly characterized regarding their physical properties, encapsulation efficiency, and cytotoxicity againts L929 cells. The antitumor activity study was then performed in mice with sarcoma 180 treated with saline, 5-fluouracil (5FU) and ERKA:β-CD at 30, 100 and 300 µg/kg. The weight, volume, percentage of inhibition growth, gross and pathological features and positivity for TUNEL, ki67, NFκB and NRF2 in the tumors were assessed. Serum lactate-dehydrogenase activity (LDH), white blood cells count (WBC) and both gross and pathological features of the liver, kidneys and spleen were also evaluated. The formation of the inclusion complexes was confirmed by thermal analysis and FTIR, and they were non-toxic for L929 cells. The MX provided a better complexation efficiency. ERKA:β-CD300 promoted significant tumor growth inhibition, and attenuated the tumor mitotic activity and necrosis content, comparable to 5-fluorouracil. ERKA:β-CD300 also increased TUNEL-detected cell death, reduced Ki67 and NF-kB immunoexpression, and partially inhibited the serum LDH activity. No side effect was observed in ERKA:β-CD300-treated animals. The ERKA:β-CD inclusion complexes at 300 µg/kg displays antitumour activity in mice with low systemic toxicity, likely due to inhibition on the NF-kB signaling pathway and LDH activity.

LDHA: The Obstacle to T cell responses against tumor

Immunotherapy has become a successful therapeutic strategy in certain solid tumors and hematological malignancies. However, this efficacy of immunotherapy is impeded by limited success rates. Cellular metabolic reprogramming determines the functionality and viability in both cancer cells and immune cells. Extensive research has unraveled that the limited success of immunotherapy is related to immune evasive metabolic reprogramming in tumor cells and immune cells. As an enzyme that catalyzes the final step of glycolysis, lactate dehydrogenase A (LDHA) has become a major focus of research. Here, we have addressed the structure, localization, and biological features of LDHA. Furthermore, we have discussed the various aspects of epigenetic regulation of LDHA expression, such as histone modification, DNA methylation, N6-methyladenosine (m6A) RNA methylation, and transcriptional control by noncoding RNA. With a focus on the extrinsic (tumor cells) and intrinsic (T cells) functions of LDHA in T-cell responses against tumors, in this article, we have reviewed the current status of LDHA inhibitors and their combination with T cell-mediated immunotherapies and postulated different strategies for future therapeutic regimens.

Tumor glycolysis, an essential sweet tooth of tumor cells

Cancer cells undergo metabolic alterations to meet the immense demand for energy, building blocks, and redox potential. Tumors show glucose-avid and lactate-secreting behavior even in the presence of oxygen, a process known as aerobic glycolysis. Glycolysis is the backbone of cancer cell metabolism, and cancer cells have evolved various mechanisms to enhance it. Glucose metabolism is intertwined with other metabolic pathways, making cancer metabolism diverse and heterogeneous, where glycolysis plays a central role. Oncogenic signaling accelerates the metabolic activities of glycolytic enzymes, mainly by enhancing their expression or by post-translational modifications. Aerobic glycolysis ferments glucose into lactate which supports tumor growth and metastasis by various mechanisms. Herein, we focused on tumor glycolysis, especially its interactions with the pentose phosphate pathway, glutamine metabolism, one-carbon metabolism, and mitochondrial oxidation. Further, we describe the role and regulation of key glycolytic enzymes in cancer. We summarize the role of lactate, an end product of glycolysis, in tumor growth, and the metabolic adaptations during metastasis. Lastly, we briefly discuss limitations and future directions to improve our understanding of glucose metabolism in cancer.

Natural products targeting human lactate dehydrogenases for cancer therapy: A mini review

Reprogramming cancer metabolism has become the hallmark of cancer progression. As the key enzyme catalyzing the conversion of pyruvate to lactate in aerobic glycolysis of cancer cells, human lactate dehydrogenase (LDH) has been a promising target in the discovery of anticancer agents. Natural products are important sources of new drugs. Up to now, some natural compounds have been reported with the activity to target LDH. To give more information on the development of LDH inhibitors and application of natural products, herein, we reviewed the natural compounds with inhibition of LDH from diverse structures and discussed the future direction of the discovery of natural LDH inhibitors for cancer therapy.

Lactate Dehydrogenase and its clinical significance in pancreatic and thoracic cancers

The energy metabolism of tumor cells is considered one of the hallmarks of cancer because it is different from normal cells and mainly consists of aerobic glycolysis, fatty acid oxidation, and glutaminolysis. It is about one hundred years ago since Warburg observed that cancer cells prefer aerobic glycolysis even in normoxic conditions, favoring their high proliferation rate. A pivotal enzyme driving this phenomenon is lactate dehydrogenase (LDH), and this review describes prognostic and therapeutic opportunities associated with this enzyme, focussing on tumors with limited therapeutic strategies and life expectancy (i.e., pancreatic and thoracic cancers). Expression levels of LDH-A in pancreatic cancer tissues correlate with clinicopathological features: LDH-A is overexpressed during pancreatic carcinogenesis and showed significantly higher expression in more aggressive tumors. Similarly, LDH levels are a marker of negative prognosis in patients with both adenocarcinoma or squamous cell lung carcinoma, as well as in malignant pleural mesothelioma. Additionally, serum LDH levels may play a key role in the clinical management of these diseases because they are associated with tissue damage induced by tumor burden. Lastly, we discuss the promising results of strategies targeting LDH as a treatment strategy, reporting recent preclinical and translational studies supporting the use of LDH-inhibitors in combinations with current/novel chemotherapeutics that can synergistically target the oxygenated cells present in the tumor.

Discovery of novel human lactate dehydrogenase inhibitors: Structure-based virtual screening studies and biological assessment

Most cancer cells switch their metabolism from mitochondrial oxidative phosphorylation to aerobic glycolysis to generate ATP and precursors for the biosynthesis of key macromolecules. The aerobic conversion of pyruvate to lactate, coupled to oxidation of the nicotinamide cofactor, is a primary hallmark of cancer and is catalyzed by lactate dehydrogenase (LDH), a central effector of this pathological reprogrammed metabolism. Hence, inhibition of LDH is a potential new promising therapeutic approach for cancer. In the search for new LDH inhibitors, we carried out a structure-based virtual screening campaign. Here, we report the identification of a novel specific LDH inhibitor, the pyridazine derivative 18 (RS6212), that exhibits potent anticancer activity within the micromolar range in multiple cancer cell lines and synergizes with complex I inhibition in the suppression of tumor growth. Altogether, our data support the conclusion that compound 18 deserves to be further investigated as a starting point for the development of LDH inhibitors and for novel anticancer strategies based on the targeting of key metabolic steps.

Design and Synthesis of New Pyrimidine-Quinolone Hybrids as Novel hLDHA Inhibitors

A battery of novel pyrimidine-quinolone hybrids was designed by docking scaffold replacement as lactate dehydrogenase A (hLDHA) inhibitors. Structures with different linkers between the pyrimidine and quinolone scaffolds (10-21 and 24−31) were studied in silico, and those with the 2-aminophenylsulfide (U-shaped) and 4-aminophenylsulfide linkers (24−31) were finally selected. These new pyrimidine-quinolone hybrids (24−31)(a−c) were easily synthesized in good to excellent yields by a green catalyst-free microwave-assisted aromatic nucleophilic substitution reaction between 3-(((2/4-aminophenyl)thio)methyl)quinolin-2(1H)-ones 22/23(a−c) and 4-aryl-2-chloropyrimidines (1−4). The inhibitory activity against hLDHA of the synthesized hybrids was evaluated, resulting IC50 values of the U-shaped hybrids 24−27(a−c) much better than the ones of the 1,4-linked hybrids 28−31(a−c). From these results, a preliminary structure−activity relationship (SAR) was established, which enabled the design of novel 1,3-linked pyrimidine-quinolone hybrids (33−36)(a−c). Compounds 35(a−c), the most promising ones, were synthesized and evaluated, fitting the experimental results with the predictions from docking analysis. In this way, we obtained novel pyrimidine-quinolone hybrids (25a, 25b, and 35a) with good IC50 values (<20 μM) and developed a preliminary SAR.

The effect of lactate dehydrogenase-A inhibition on intracellular nucleotides and mitochondrial respiration in pancreatic cancer cells

Pancreatic cancer (PC) is one of the most lethal malignancies. PC is characterized by a high expression of the glucose transporter GLUT-1 and of lactate dehydrogenase A (LDH-A). The novel LDH-A inhibitor NHI-Glc-2 was designed for a better uptake via GLUT-1 and was shown to be cytotoxic against the PC cell line PANC-1. Using RP-HPLC we investigated its effect on adenine nucleotides and NADH/NAD+, while the Seahorse analyzer was used to determine its effect on glycolysis and mitochondrial function. A 24 hour exposure to 10 µM NHI-Glc-2 (around the IC50) decreased the ATP concentration by about 10%, but at 25 µM this decrease was 38%, while NAD+ decreased by 26%, associated with a 35% decrease in the NADH/NAD+ ratio. A 10 µM NHI-Glc-2 decreased extracellular acidification and oxygen consumption (about 75%), as well as the mitochondrial respiration parameters by 50%. In conclusion, LDH-A inhibition markedly affected the energy supply of PANC-1 cells. The respiration data indicated a dependency of the cells on glycolysis and fatty acid oxidation.Supplemental data for this article is available online at https://doi.org/10.1080/15257770.2022.2031215 .

Targeting glucose metabolism to develop anticancer treatments and therapeutic patents

INTRODUCTION

One of the most distinctive hallmarks of cancer cells is increased glucose consumption for aerobic glycolysis which is named the Warburg effect. In recent decades, extensive research has been carried out to exploit this famous phenomenon, trying to detect promising targetable vulnerabilities in altered metabolism to fight cancer. Targeting aberrant glucose metabolism can perturb cancer malignant proliferation and even induce programmed cell death.

AREAS COVERED

This review covered the recent patents which focused on targeting key glycolytic enzymes including hexokinase, pyruvate dehydrogenase kinases and lactate dehydrogenase for cancer treatment.

EXPERT OPINION

Compared with the conventional cancer treatment, specifically targeting the well-known Achilles heel Warburg effect has attracted considerable attention. Although there is still no single glycolytic agent for clinical cancer treatment, the combination of glycolytic inhibitor with conventional anticancer drug or the combined use of multiple glycolytic inhibitors are being investigated extensively in recent years, which could emerge as attractive anticancer strategies.

Synergistic Effect of Repolarization of M2 to M1 Macrophages Induced by Iron Oxide Nanoparticles Combined with Lactate Oxidase

Metabolic reprogramming of tumors with the accompanying reprogramming of glucose metabolism and production of lactate accumulation is required for the subsequent development of tumors. Recent evidence has indicated that tumor-secreted lactate can promote an oncolytic immune microenvironment within the tumor. Furthermore, tumor-secreted lactate directly induces polarization of tumor-supportive M2 macrophages. However, oxidized tumor-secreted lactate in the tumor microenvironment can be exploited. Iron oxide nanoparticles have shown promising anticancer potential by activating tumor-suppressing macrophages. Furthermore, lactate oxidase (LOX) generally oxidizes tumor-secreted lactate and subsequently converts to pyruvate. Particularly, the ratio of M2 macrophages to M1 macrophages corresponds with tumor growth. In this study, we present iron oxide nanoparticles with carboxylic acid combined with LOX that enhance antitumor efficacy as a synergistic effect on the repolarization of tumor-supportive M2 macrophages to tumor-suppressive M1 macrophages in a tumor microenvironment. After M2 macrophages treated with iron oxide nanoparticles were combined with LOX, the ratio of M1 macrophages was significantly greater than iron oxide nanoparticles alone or with LOX alone. It is concluded that the inhibition of cancer cell proliferation by ratio of M1 macrophages was observed. This study suggests that the iron oxide nanoparticles combined with LOX could be potentially used for potentiating immune checkpoint inhibitor therapies for cancer treatment.

Targeting cancer metabolism in the era of precision oncology

One hundred years have passed since Warburg discovered alterations in cancer metabolism, more than 70 years since Sidney Farber introduced anti-folates that transformed the treatment of childhood leukaemia, and 20 years since metabolism was linked to oncogenes. However, progress in targeting cancer metabolism therapeutically in the past decade has been limited. Only a few metabolism-based drugs for cancer have been successfully developed, some of which are in - or en route to - clinical trials. Strategies for targeting the intrinsic metabolism of cancer cells often did not account for the metabolism of non-cancer stromal and immune cells, which have pivotal roles in tumour progression and maintenance. By considering immune cell metabolism and the clinical manifestations of inborn errors of metabolism, it may be possible to isolate undesirable off-tumour, on-target effects of metabolic drugs during their development. Hence, the conceptual framework for drug design must consider the metabolic vulnerabilities of non-cancer cells in the tumour immune microenvironment, as well as those of cancer cells. In this Review, we cover the recent developments, notable milestones and setbacks in targeting cancer metabolism, and discuss the way forward for the field.

Ethoxyquin Inhibits the Progression of Murine Ehrlich Ascites Carcinoma through the Inhibition of Autophagy and LDH

Cancer cells exhibit an increased glycolysis rate for ATP generation (the Warburg effect) to sustain an increased proliferation rate. In tumor cells, the oxidation of pyruvate in the Krebs cycle is substituted by lactate production, catalyzed by LDH. In this study, we use ethoxyquin (EQ) as a novel inhibitor to target LDH in murine Ehrlich ascites carcinoma (EAC) and as a combination therapy to improve the therapeutic efficacy of the conventional chemotherapy drug, cisplatin (CIS). We investigated the anti-tumor effect of EQ on EAC-bearing mice and checked whether EQ can sustain the anti-tumor potential of CIS and whether it influences LDH activity. Treatment with EQ had evident anti-tumor effects on EAC as revealed by the remarkable decrease in the expression of the anti-apoptotic gene Bcl-2 and by a significant increase in the expression of apoptotic genes (BAX and caspase-3). EQ also caused a significant decrease in the autophagic activity of EAC cells, as shown by a reduction in the fluorescence intensity of the autophagosome marker. Additionally, EQ restored the altered hematological and biochemical parameters and improved the disrupted hepatic tissues of EAC-bearing mice. Co-administration of EQ and CIS showed the highest anti-tumor effect against EAC. Collectively, our findings propose EQ as a novel inhibitor of LDH in cancer cells and as a combinatory drug to increase the efficacy of cisplatin. Further studies are required to validate this therapeutic strategy in different cancer models and preclinical trials.

Lactate shuttle: from substance exchange to regulatory mechanism

Lactate, as the product of glycolytic metabolism and the substrate of energy metabolism, is an intermediate link between cancer cell and tumor microenvironment metabolism. The exchange of lactate between the two cells via mono-carboxylate transporters (MCTs) is known as the lactate shuttle in cancer. Lactate shuttle is the core of cancer cell metabolic reprogramming between two cells such as aerobic cancer cells and hypoxic cancer cells, tumor cells and stromal cells, cancer cells and vascular endothelial cells. Cancer cells absorb lactate by mono-carboxylate transporter 1 (MCT1) and convert lactate to pyruvate via intracellular lactate dehydrogenase B (LDH-B) to maintain their growth and metabolism. Since lactate shuttle may play a critical role in energy metabolism of cancer cells, components related to lactate shuttle may be a crucial target for tumor antimetabolic therapy. In this review, we describe the lactate shuttle in terms of both substance exchange and regulatory mechanisms in cancer. Meanwhile, we summarize the difference of key proteins of lactate shuttle in common types of cancer.

Phylogenetics and biochemistry elucidate the evolutionary link between l-malate and l-lactate dehydrogenases and disclose an intermediate group of sequences with mix functional properties

The NAD(P)-dependent malate dehydrogenases (MDH) (EC 1.1.1.37) and NAD-dependent lactate dehydrogenases (LDH) (EC. 1.1.1.27) form a large superfamily that has been characterized in organisms belonging to the three Domains of Life. MDH catalyzes the reversible conversion of the oxaloacetate into malate, while LDH operates at the late stage of glycolysis by converting pyruvate into lactate. Phylogenetic studies proposed that the LDH/MDH superfamily encompasses five main groups of enzymes. Here, starting from 16,052 reference proteomes, we reinvestigated the relationships between MDH and LDH. We showed that the LDH/MDH superfamily encompasses three main families: MDH1, MDH2, and a large family encompassing MDH3, LDH, and L-2-hydroxyisocaproate dehydrogenases (HicDH) sequences. An in-depth analysis of the phylogeny of the MDH3/LDH/HicDH family and of the nature of three important amino acids, located within the catalytic site and involved in binding and substrate discrimination, revealed a large group of sequences displaying unexpected combinations of amino acids at these three critical positions. This group branched in-between canonical MDH3 and LDH sequences. The functional characterization of several enzymes from this intermediate group disclosed a mix of functional properties, indicating that the MDH3/LDH/HicDH family is much more diverse than previously thought, and blurred the frontier between MDH3 and LDH enzymes. Present-days enzymes of the intermediate group are a valuable material to study the evolutionary steps that led to functional diversity and emergence of allosteric regulation within the LDH/MDH superfamily.

Potential therapeutics using tumor-secreted lactate in nonsmall cell lung cancer

Targeted-therapy failure in treating nonsmall cell lung cancer (NSCLC) frequently occurs because of the emergence of drug resistance and genetic mutations. The same mutations also result in aerobic glycolysis, which further antagonizes outcomes by localized increases in lactate, an immune suppressor. Recent evidence indicates that enzymatic lowering of lactate can promote an oncolytic immune microenvironment within the tumour. Here, we review factors relating to lactate expression in NSCLC and the utility of lactate oxidase (LOX) for governing therapeutic delivery, its role in lactate oxidation and turnover, and relationships between lactate depletion and immune cell populations. The lactate-rich characteristic of NSCLC provides an exploitable property to potentially improve NSCLC outcomes and design new therapeutic strategies to integrate with conventional therapies.

Profiling the interaction of a novel toxic pyruvate dehydrogenase kinase inhibitor with human serum albumin

To discover novel pyruvate dehydrogenase kinase (PDK) inhibitors, a new compound 2,2-dichloro-1-(4-((4-isopropylphenyl)amino)-3-nitrophenyl)ethan-1-one, namely XB-1 was identified, which inhibited PDK activity with a half maximal inhibitory concentration (IC₅₀) value of 337.0 nM, and reduced A549 cell proliferation with a half maximal effective concentration (EC₅₀) value of 330.0 nM. However, the compound appears to exhibit a negligible selectivity between cancer cell and normal one, indicating a potential toxicity existed for the compound. Herein, the interaction of the toxic XB-1 to human serum albumin (HSA) was firstly explored by spectroscopic approaches with the aim to reduce/avoid the toxicity of PDK inhibitors in the next hit-to-lead campaign. In detail, it was found that the XB-1 could effectively bind to HSA mainly via hydrogen bond interaction in PBS buffer (pH = 7.4, 10.0 mM), resulting in the formation of HSA-XB-1 complex. The negative value of ΔG showed that the binding of XB-1 to HSA is a spontaneous process. The result from site-selective binding assay suggested that the XB-1 bound to the site I of HSA by competing with warfarin, which was perfect in agreement with the molecular docking method. The results of this paper may offer a valuable theoretical basis to study the toxicity of biofunctional molecules and may offer thoughts about how to avoid/reduce toxicity for a small molecule.

A Scoring System Based on Nutritional and Inflammatory Parameters to Predict the Efficacy of First-Line Chemotherapy and Survival Outcomes for De Novo Metastatic Nasopharyngeal Carcinoma

Purpose

We aimed to develop a simple scoring system based on baseline inflammatory and nutritional parameters to predict the efficacy of first-line chemotherapy and survival outcomes for de novo metastatic nasopharyngeal carcinoma (mNPC).

Patients and Methods

We retrospectively collected ten candidate inflammatory and nutritional parameters from de novo mNPC patients who received platinum-based first-line chemotherapy treatment. We examined the effects of these ten candidate variables on progression-free survival (PFS) using the Cox regression model. We built a risk-scoring system based on the regression coefficients associated with the identified independent prognostic factors. The predictive accuracy of the scoring system was evaluated and independently validated.

Results

A total of 460 patients were analyzed. Four independent prognostic factors were identified in a training cohort and were used to construct the scoring system, including nutritional risk index, C-reactive protein level, alkaline phosphatase level, and lactate dehydrogenase level. Based on the score obtained from the scoring system, we stratified patients into three prognostic subgroups (low: 0–1 point, intermediate: 2–3 points, and high: 4 points) associated with significantly different disease control rates (94.7% vs. 92.5% vs. 66.0%, respectively) and survival outcomes (3-year PFS: 55.8% vs. 29.1% vs. 11.9%, respectively). The scoring system had a good performance for the prediction of short-term disease control (area under the receiver operating characteristic curve [AUC]: 0.701) and long-term survival outcomes (time-dependent AUC for 5-year PFS: 0.713). The results were internally validated using an independent cohort (AUC for predicting disease control: 0.697; time-dependent AUC for 5-year PFS: 0.713).

Conclusion

We developed and validated a clinically useful risk-scoring system that could predict the efficacy of first-line chemotherapy and survival outcomes in de novo mNPC patients. This system may help clinicians to design personalized treatment strategies.

Small Molecule-Based Enzyme Inhibitors in the Treatment of Primary Hyperoxalurias

Primary hyperoxalurias (PHs) are a group of inherited alterations of the hepatic glyoxylate metabolism. PHs classification based on gene mutations parallel a variety of enzymatic defects, and all involve the harmful accumulation of calcium oxalate crystals that produce systemic damage. These geographically widespread rare diseases have a deep impact in the life quality of the patients. Until recently, treatments were limited to palliative measures and kidney/liver transplants in the most severe forms. Efforts made to develop pharmacological treatments succeeded with the biotechnological agent lumasiran, a siRNA product against glycolate oxidase, which has become the first effective therapy to treat PH1. However, small molecule drugs have classically been preferred since they benefit from experience and have better pharmacological properties. The development of small molecule inhibitors designed against key enzymes of glyoxylate metabolism is on the focus of research. Enzyme inhibitors are successful and widely used in several diseases and their pharmacokinetic advantages are well known. In PHs, effective enzymatic targets have been determined and characterized for drug design and interesting inhibitory activities have been achieved both in vitro and in vivo. This review describes the most recent advances towards the development of small molecule enzyme inhibitors in the treatment of PHs, introducing the multi-target approach as a more effective and safe therapeutic option.

Tetrazanbigen Derivatives as Peroxisome Proliferator-Activated Receptor Gamma (PPARγ) Partial Agonists: Design, Synthesis, Structure-Activity Relationship, and Anticancer Activities

Tetrazanbigen (TNBG) is a novel sterol isoquinoline derivative with poor water solubility and moderate inhibitory effects on human cancer cell lines via lipoapoptosis induction. Herein, we developed a series of novel TNBG analogues with improved water solubility and antiproliferative activities. The CCK-8 assay enabled us to identify a novel compound, 14g, which strongly inhibited HepG2 and A549 cell growth with IC₅₀ values of 0.54 and 0.47 μM, respectively. The anticancer effects might be explained by the partial activation and upregulation of PPARγ expression, as indicated by the transactivation assay and western blotting evaluation. Furthermore, the in vitro antiproliferative activity was verified in an in vivo xenograft model in which 14g strongly reduced tumor growth at a dose of 10 mg/kg. In line with these positive observations, 14g exhibited an excellent water solubility of 31.4 mg/mL, which was more than 1000-fold higher than that of TNBG (4 μg/mL). Together, these results suggest that 14g is a promising anticancer therapeutic that deserves further investigation.

Lactate dehydrogenase inhibition affects homologous recombination repair independently of cell metabolic asset; implications for anticancer treatment

BACKGROUND

Cancer cells show highly increased glucose utilization which, among other cancer-essential functions, was found to facilitate DNA repair. Lactate dehydrogenase (LDH) activity is pivotal for supporting the high glycolytic flux of cancer cells; to our knowledge, a direct contribution of this enzyme in the control of DNA integrity was never investigated. In this paper, we looked into a possible LDH-mediated regulation of homologous recombination (HR) repair.

METHODS

We identified two cancer cell lines with different assets in energy metabolism: either based on glycolytic ATP or on oxidative reactions. In cells with inhibited LDH, we assessed HR function by applying four different procedures.

RESULTS

Our findings revealed an LDH-mediated control of HR, which was observed independently of cell metabolic asset. Since HR inhibition is known to make cancer cells responsive to PARP inhibitors, in both the cellular models we finally explored the effects of a combined inhibition of LDH and PARP.

CONCLUSIONS

The obtained results suggest for LDH a central role in cancer cell biology, not merely linked to the control of energy metabolism. The involvement of LDH in the DNA damage response could suggest new drug combinations to obtain improved antineoplastic effects.

GENERAL SIGNIFICANCE

Several evidences have correlated the metabolic features of cancer cells with drug resistance and LDH inhibition has been repeatedly shown to increase the antineoplastic power of chemotherapeutics. By shedding light on the processes linking cell metabolism to the control of DNA integrity, our findings also give a mechanistic explanation to these data.

Structural Evidence for Isoform-Selective Allosteric Inhibition of Lactate Dehydrogenase A

Lactate dehydrogenase A (LDHA) is frequently overexpressed in tumors, thereby sustaining high glycolysis rates, tumor growth, and chemoresistance. High-throughput screening resulted in the identification of phthalimide and dibenzofuran derivatives as novel lactate dehydrogenase inhibitors, selectively inhibiting the activity of the LDHA isoenzyme. Cocrystallization experiments confirmed target engagement in addition to demonstrating binding to a novel allosteric binding site present in all four LDHA subunits of the LDH5 homotetramer.

Lactate dehydrogenase: a marker of diminished antitumor immunity

Lactate dehydrogenase (LDH) levels are inversely related with response to checkpoint inhibitors. Elevated LDH levels are the product of enhanced glycolytic activity of the tumor and tumor necrosis due to hypoxia, the latter being associated with high tumor burden. In this review, we elucidate the effects of glycolysis and hypoxia on antitumor immunity and set forth ways to improve response to immunotherapy in cancer patients with elevated LDH levels. We discuss the current knowledge on combining immunotherapy with glycolysis inhibitors, anti-acidifying drugs, anti-angiogenic or cytoreductive therapy.

Structural and functional regulation of lactate dehydrogenase-A in cancer

Dysregulated metabolism is one of the hallmarks of cancer. Under normal physiological conditions, ATP is primarily generated by oxidative phosphorylation. Cancers commonly undergo a dramatic shift toward glycolysis, despite the presence of oxygen. This phenomenon is known as the Warburg effect, and requires the activity of LDHA. LDHA converts pyruvate to lactate in the final step of glycolysis and is often upregulated in cancer. LDHA inhibitors present a promising therapeutic option, as LDHA blockade leads to apoptosis in cancer cells. Despite this, existing LDHA inhibitors have shown limited clinical efficacy. Here, we review recent progress in LDHA structure, function and regulation as well as strategies to target this critical enzyme.

Identification of human lactate dehydrogenase A inhibitors with anti-osteosarcoma activity through cell-based phenotypic screening

Human lactate dehydrogenase A plays a key role in the glycolytic process, the inhibition of the enzyme is therefore considered of interest in developing anticancer therapeutics. However, due to the highly polar nature of hLDHA binding pocket, it is very challenge to discover potent cellular active hLDHA inhibitor. Combined a cell-based phenotypic screening assay with a primary enzymatic assay, we discovered three cellular active hLDHA inhibitors, namely 38, 63, and 374, which reduced MG-63 cell proliferation with IC₅₀ values of 6.47, 2.93, and 6.10 µM, respectively, and inhibited hLDHA with EC₅₀ values of 3.03, 0.63, and 3.26 µM, respectively.

Discovery of human lactate dehydrogenase 5 inhibitors (hLDH5) with anti-lung cancer activity through an in silico method and biological validation

Human lactate dehydrogenase 5 (hLDH5) is an important metabolic enzyme playing critical roles in the anaerobic glycolysis. Herein, we employed an in silico method and biological validation to identify a novel hLDH5 inhibitor with a promising cellular activity under hypoxia condition. The identified compound 9 bound to hLDH5 with a K_d value of 1.02 µM, and inhibited the enzyme with an EC₅₀ value of 0.7 µM. Compound 9 exhibited a weak potency against NCI-H1975 cell proliferation under normal condition (IC₅₀ = 36.5 µM), while dramatically increased to 5.7 µM under hypoxia condition. In line with the observation, hLDH5 expression in NCI-H1975 cell under hypoxia condition is much higher as compared to the normal oxygenated condition, indicating the hLDH5 inhibition may contribute to the cancer cell death.

Therapeutic targeting of glutaminolysis as an essential strategy to combat cancer

Metabolic reprogramming in cancer targets glutamine metabolism as a key mechanism to provide energy, biosynthetic precursors and redox requirements to allow the massive proliferation of tumor cells. Glutamine is also a signaling molecule involved in essential pathways regulated by oncogenes and tumor suppressor factors. Glutaminase isoenzymes are critical proteins to control glutaminolysis, a key metabolic pathway for cell proliferation and survival that directs neoplasms' fate. Adaptive glutamine metabolism can be altered by different metabolic therapies, including the use of specific allosteric inhibitors of glutaminase that can evoke synergistic effects for the therapy of cancer patients. We also review other clinical applications of in vivo assessment of glutaminolysis by metabolomic approaches, including diagnosis and monitoring of cancer.

A noncoding RNA LINC00504 interacts with c-Myc to regulate tumor metabolism in colon cancer

Accumulating evidence has shown a critical role of long-non-coding RNAs (lncRNAs) during multiple tumor progression. However, the potential functions of LINC00504 in colon cancer as well as its mechanisms remain obscure. By lncRNA profiling, we identified LINC00504 as a novel oncogenic lncRNA in colon cancer. The lncRNA LINC00504 was markedly upregulated in colon cancer cell lines and specimens. LINC00504 increases viability and migration of colon cells in vitro. Furthermore, LINC00504 also enhances colon cancer xenograft tumors in vivo. We noted that LINC00504 regulates metabolism at a transcriptional level which influences multiple metabolic pathways, such as glucose metabolism, pentose phosphate pathway, and tricarboxylic acid cycle. Mechanistic study showed that LINC00504 could interact with c-Myc to promote chromatin recruitment of c-Myc and enhance its transactivation activity. Collectively, our results showed that LINC00504 serves as an important transcriptional regulator for c-Myc in colon cancer cells. LINC00504 can reprogram central metabolism in colon cancer cells implying that LINC00504 may serve as a potential target for therapeutic intervention.

Metabolic activation triggered by cAMP in MCF-7 cells generates lethal vulnerability to combined oxamate/etomoxir

BACKGROUND

Altered energy metabolism is a biochemical fingerprint of cancer cells, widely recognized as one of the "hallmarks of cancer". Cancer cells show highly increased rates of glucose uptake and glycolysis, after which the resulting pyruvate is converted to lactate. The maintenance of this metabolic asset is warranted by lactate dehydrogenase A (LDH-A) and for this reason the development of novel LDH-targeted anticancer therapeutics is underway. However, possible interference in cancer cell metabolism could also arise from cAMP signaling pathway, which could be activated by either oncogenic induction or exogenously, as a result of microenvironment-derived stimuli, increasing cellular cAMP levels. This study aimed at evaluating the impact of activated cAMP signaling pathway on the efficacy of an LDH-targeted anticancer approach.

METHODS

We exogenously activated cAMP signaling in MCF-7 human breast cancer cells and explored the metabolic interplay between LDH-A and cAMP pathway.

RESULTS

In cAMP-activated cells, we evidenced changes in energy metabolism which reduced their response to LDH inhibition. Interestingly, these experiments also highlighted a potential vulnerability state of treated cells.

CONCLUSIONS

cAMP-induced metabolic changes made MCF-7 cells a preferential target of a drug combination treatment which should not affect normal cell viability.

GENERAL SIGNIFICANCE

cAMP is a well-recognized second messenger of the pro-inflammatory cascade. The obtained results are relevant in consideration of the crucial role played by inflammation in normal breast cell transformation and in cancer progression. Furthermore, they corroborate the idea of exploiting the metabolic changes observed in cancer cells to obtain a therapeutic advantage.