Lactate Dehydrogenase A Activity Research Articles

Proteomic identification of the lactate dehydrogenase A in a radioresistant prostate cancer xenograft mouse model for improving radiotherapy

Radioresistance is a major challenge for prostate cancer (CaP) metastasis and recurrence after radiotherapy. This study aimed to identify potential protein markers and signaling pathways associated with radioresistance using a PC-3 radioresistant (RR) subcutaneous xenograft mouse model and verify the radiosensitization effect from a selected potential candidate. PC-3RR and PC-3 xenograft tumors were established and differential protein expression profiles from two groups of xenografts were analyzed using liquid chromatography tandem-mass spectrometry. One selected glycolysis marker, lactate dehydrogenase A (LDHA) was validated, and further investigated for its role in CaP radioresistance. We found that 378 proteins and 51 pathways were significantly differentially expressed between PC-3RR and PC-3 xenograft tumors, and that the glycolysis pathway is closely linked with CaP radioresistance. In addition, we also demonstrated that knock down of LDHA with siRNA or inhibition of LDHA activity with a LDHA specific inhibitor (FX-11), could sensitize PC-3RR cells to radiotherapy with reduced epithelial-mesenchymal transition, hypoxia, DNA repair ability and autophagy, as well as increased DNA double strand breaks and apoptosis. In summary, we identified a list of potential RR protein markers and important signaling pathways from a PC-3RR xenograft mouse model, and demonstrate that targeting LDHA combined with radiotherapy could increase radiosensitivity in RR CaP cells, suggesting that LDHA is an ideal therapeutic target to develop combination therapy for overcoming CaP radioresistance.

Sirtuin 6 suppresses hypoxia-induced inflammatory response in human osteoblasts via inhibition of reactive oxygen species production and glycolysis-A therapeutic implication in inflammatory bone resorption.

Elevated glycolytic activity and redox imbalance induced by tissue hypoxia are common phenomena of chronic inflammation, including inflammatory bone diseases such as arthritis. However, relation between glycolysis and redox signaling in the inflammatory milieu is unclear. The histone deacetylase sirtuin 6 (SIRT6) is a crucial modulator of inflammation and glucose metabolism, and it is also involved in cellular protection against oxidative injury. The aims of the study were to examine the connection between glycolysis and reactive oxygen species (ROS) production in human osteoblastic cells (HOB) and whether SIRT6 modulates inflammatory response via regulation of glycolytic activity and ROS generation. In HOB cultured under hypoxia, expression of lactate dehydrogenase A (LDHA), lactate production and ROS generation were examined. The reciprocal effects between lactate and ROS production and their impact on inflammatory cytokine induction were assessed. The action of SIRT6 on the above reactions was determined. In a rat model of collagen-induced arthritis (CIA), the relation between inflammatory activity and osteoblastic expression of LDHA, level of oxidative lesions, Cyr61 synthesis and macrophage recruitment were examined in joints with or without lentiviral-SIRT6 gene therapy. Results showed that hypoxia stress enhanced lactate and LDHA production in HOB. ROS generation was also increased, and there was a positive feedback between glycolysis and ROS formation. Overexpression of SIRT6 attenuated hypoxia-enhanced glycolysis and ROS generation. Hypoxia-induced expressions of Cyr61, TNF-α, IL-1β, and IL-6 were suppressed by SIRT6 and the inhibitory effects overlapped with antiglycolytic and antioxidation mechanisms. In the model of CIA, forced expression of SIRT6 ameliorated disease progression, osteoblastic synthesis of Cyr61, and macrophage recruitment. More importantly, expression of LDHA and oxidative lesions were decreased in osteoblasts of SIRT6-treated joints. Our findings suggest that SIRT6 suppresses inflammatory response in osteoblasts via modulation of glucose metabolism and redox homeostasis. SIRT6-based strategy may possess therapeutic potential for inflammatory bone resorption. © 2016 BioFactors, 43(2):170-180, 2017.

Pharmacological or genetic inhibition of LDHA reverses tumor progression of pediatric osteosarcoma

Reprogrammed energy metabolism is an emerging hallmark of cancer. Lactate dehydrogenase A (LDHA), a key enzyme involved in anaerobic glycolysis, is frequently deregulated in human malignancies. However, limited knowledge is known about its roles in the progression of osteosarcoma (OS). In this study, we found that LDHA is commonly upregulated in four OS cell lines compared with the normal osteoblast cells (hFOB1.19). Treatment with FX11, a specific inhibitor of LDHA, significantly reduced LDHA activity, and inhibited cell proliferation and invasive potential in a dose dependent manner. Genetic silencing of LDHA resulted in a decreased lactate level in the culture medium, reduced cell viability and decreased cell invasion ability. Meanwhile, silencing of LDHA also compromised tumorigenesis in vivo. Furthermore, knockdown of LDHA remarkably reduced extracellular acidification rate (ECAR) as well as glucose consumption. In the presence of 2-DG, a glycolysis inhibitor, LDHA-mediated cell proliferation and invasion were completely blocked, indicating the oncogenic activities of LDHA may dependent on Warburg effect. Finally, pharmacological inhibition of c-Myc or HIF1α significantly attenuated LDHA expression. Taken together, upregulated LDHA facilitates tumor progression of OS and might be a potential target for OS treatment.

Evaluation on the inhibition of pyrrol-2-yl ethanone derivatives to lactate dehydrogenase and anticancer activities

Lactate dehydrogenase A (LDH-A) is a potentially important metabolic target for the inhibition of the highly activated glycolysis pathway in cancer cells. In order to develop bifunctional compounds as inhibitor of LDH-A and anticancer agents, two pyrrol-2-yl methanone (or ethanone) derivatives (PM1 and PM2) were synthesized and evaluated as inhibitors of LDH-A based on the enzyme assay and cell assay by spectroscopy analysis. Fluorescence and CD spectra results demonstrated that both the change of second structure of LDH-A and the affinity interaction for compounds to LDH-A gave great effect on the activity of LDH-A. In particular, low concentration of compounds (1μμ–25μμ) could change the level of pyruvate in cancer cells. Moreover, the in vitro assay results demonstrated that pyrrol-2-yl ethanone derivatives can inhibit the proliferation of cancer cells. Therefore, pyrrol-2-yl ethanone derivatives (PM2) can be both LDH-A inhibitor and anticancer agents.

Proteomic Assessment of the Relevant Factors Affecting Pork Meat Quality Associated with Longissimus dorsi Muscles in Duroc Pigs.

Meat quality is a complex trait influenced by many factors, including genetics, nutrition, feeding environment, animal handling, and their interactions. To elucidate relevant factors affecting pork quality associated with oxidative stress and muscle development, we analyzed protein expression in high quality longissimus dorsi muscles (HQLD) and low quality longissimus dorsi muscles (LQLD) from Duroc pigs by liquid chromatographytandem mass spectrometry (LC-MS/MS)–based proteomic analysis. Between HQLD (n = 20) and LQLD (n = 20) Duroc pigs, 24 differentially expressed proteins were identified by LC-MS/MS. A total of 10 and 14 proteins were highly expressed in HQLD and LQLD, respectively. The 24 proteins have putative functions in the following seven categories: catalytic activity (31%), ATPase activity (19%), oxidoreductase activity (13%), cytoskeletal protein binding (13%), actin binding (12%), calcium ion binding (6%), and structural constituent of muscle (6%). Silver-stained image analysis revealed significant differential expression of lactate dehydrogenase A (LDHA) between HQLD and LQLD Duroc pigs. LDHA was subjected to in vitro study of myogenesis under oxidative stress conditions and LDH activity assay to verification its role in oxidative stress. No significant difference of mRNA expression level of LDHA was found between normal and oxidative stress condition. However, LDH activity was significantly higher under oxidative stress condition than at normal condition using in vitro model of myogenesis. The highly expressed LDHA was positively correlated with LQLD. Moreover, LDHA activity increased by oxidative stress was reduced by antioxidant resveratrol. This paper emphasizes the importance of differential expression patterns of proteins and their interaction for the development of meat quality traits. Our proteome data provides valuable information on important factors which might aid in the regulation of muscle development and the improvement of meat quality in longissimus dorsi muscles of Duroc pigs under oxidative stress conditions.

Overexpression of ABCC3 promotes cell proliferation, drug resistance, and aerobic glycolysis and is associated with poor prognosis in urinary bladder cancer patients.

Human urinary bladder cancer (UBC) is the one of the most common malignancies worldwide and occurs at a higher frequency in male individuals. ATP-binding cassette, subfamily C, member 3 (ABCC3), a member of the ABC transporter family, is highly expressed in tumor cells, where it actively effluxes a broad spectrum of metabolites. However, the expression and role of ABCC3 in human UBC remains unclear. Our study aimed to identify the expression status of ABCC3 in UBC cases and investigate the biological effects on UBC in cells. We found that both mRNA and protein levels of ABCC3 were significantly higher in UBC tissues than normal tissues. Immunochemistry evaluation of ABCC3 expression in 122 UBC clinical specimens showed that high expression of ABCC3 had a positive correlation with UBC tumor size, advanced tumor node metastasis stage, and malignant histology. Moreover, high ABCC3 expression was linked to poor overall survival in UBC. ABCC3 effects on cell proliferation and drug resistance were measured by colony formation and methylthiazolyldiphenyl-tetrazolium bromide (MTT) assays. ABCC3-knockdown cells showed a significant decrease in cell growth and drug resistance. RNA interference of ABCC3 also caused downregulation of lactate dehydrogenase A (LDHA), which positively correlated with ABCC3 expression in UBC specimens. In addition, cancer cell glycolytic ability was decreased upon ABCC3 knockdown. The activity of LDHA was also abrogated in ABCC3-deficient UBC cells, and the blockade of LDHA increased UBC cells sensitivity to Cis-diamine dichloroplatinum (CDDP). In summary, our study suggests ABCC3 is an important oncoprotein involved in glycolysis and drug resistance. These data also indicates that ABCC3 could be a potential prognostic marker and promising therapeutic target in UBC.

OP53INHIBITION OF LACTATE DEHYDROGENASE A (LDHA) USING SODIUM OXAMATE LEADS TO METABOLIC CHANGES, DECREASED GROWTH AND MIGRATION IN MEDULLOBLASTOMA CELL LINES

Integrated genomic data has identified four distinct Medulloblastoma (MB) sub-groups differing in clinical outcomes, of which group 3 is the most frequently metastatic and characteristically over-expresses cMyc. Lactate dehydrogenase A (LDHA), known for its key role in metabolic functions, is a downstream target of cMyc and HIF1α. We hypothesised LDHA inhibition would influence a change from a glycolytic to an oxidative phosphorylation phenotype, thus leading to decreased MB viability and migration. LDHA protein was examined in MB cell lines (Res256 and UW402) using IHC, Flow cytometry and Western blot. Lactate and pyruvate concentrations, viability, and proliferation were evaluated in the presence or absence of sodium oxamate under normoxic and hypoxic conditions. MB migration (gap-closure) and distance travelled (cell-tracking) was measured using live cell imaging. LDHA expression was elevated under hypoxic conditions in MB cells. LDHA activity was inhibited by sodium oxamate causing a concentration and time dependent decrease in lactate concentration. Significance varied depending on normoxic versus hypoxic conditions (p < 0.05-p < 0.001). Under hypoxic conditions, pyruvate levels also decreased with LDHA inhibition (p < 0.05). Sodium oxamate significantly reduced proliferation and increased the percentage of MB cells in G2/M cell cycle phase. Sodium oxamate treatment also caused a significant decrease in MB migration in a concentration/time dependent manner that was not dependent on reduced proliferation. Inhibition of LDHA activity by sodium oxamate significantly decreased lactate concentrations and significantly inhibited MB migration and proliferation. Targeting MB metabolism through LDHA is a promising approach, which could prevent the use of harsh therapy regimens, and warrants further investigation.

Ibuprofen and Diclofenac Restrict Migration and Proliferation of Human Glioma Cells by Distinct Molecular Mechanisms.

BackgroundNon-steroidal anti-inflammatory drugs (NSAIDs) have been associated with anti-tumorigenic effects in different tumor entities. For glioma, research has generally focused on diclofenac; however data on other NSAIDs, such as ibuprofen, is limited. Therefore, we performed a comprehensive investigation of the cellular, molecular, and metabolic effects of ibuprofen and diclofenac on human glioblastoma cells.MethodsGlioma cell lines were treated with ibuprofen or diclofenac to investigate functional effects on proliferation and cell motility. Cell cycle, extracellular lactate levels, lactate dehydrogenase-A (LDH-A) expression and activity, as well as inhibition of the Signal Transducer and Activator of Transcription 3 (STAT-3) signaling pathway, were determined. Specific effects of diclofenac and ibuprofen on STAT-3 were investigated by comparing their effects with those of the specific STAT-3 inhibitor STATTIC.ResultsIbuprofen treatment led to a stronger inhibition of cell growth and migration than treatment with diclofenac. Proliferation was affected by cell cycle arrest at different checkpoints by both agents. In addition, diclofenac, but not ibuprofen, decreased lactate levels in all concentrations used. Both decreased STAT-3 phosphorylation; however, diclofenac led to decreased c-myc expression and subsequent reduction in LDH-A activity, whereas treatment with ibuprofen in higher doses induced c-myc expression and less LDH-A alteration.ConclusionsThis study indicates that both ibuprofen and diclofenac strongly inhibit glioma cells, but the subsequent metabolic responses of both agents are distinct. We postulate that ibuprofen may inhibit tumor cells also by COX- and lactate-independent mechanisms after long-term treatment in physiological dosages, whereas diclofenac mainly acts by inhibition of STAT-3 signaling and downstream modulation of glycolysis.

SIRT3 Enhances Glycolysis and Proliferation in SIRT3-Expressing Gastric Cancer Cells.

SIRT3 is a key NAD+-dependent protein deacetylase in the mitochondria of mammalian cells, functioning to prevent cell aging and transformation via regulation of mitochondrial metabolic homeostasis. However, SIRT3 is also found to express in some human tumors; its role in these SIRT3-expressing tumor cells needs to be elucidated. This study demonstrated that the expression of SIRT3 was elevated in a group of gastric cancer cells compared to normal gastric epithelial cells. Although SIRT3 expression levels were increased in the gastric tumor tissues compared to the adjacent non-tumor tissues, SIRT3 positive cancer cells were more frequently detected in the intestinal type gastric cancers than the diffuse type gastric cancers, indicating that SIRT3 is linked with subtypes of gastric cancer. Overexpression of SIRT3 promoted cell proliferation and enhanced ATP generation, glucose uptake, glycogen formation, MnSOD activity and lactate production, which were inhibited by SIRT3 knockdown, indicating that SIRT3 plays a role in reprogramming the bioenergetics in gastric tumor cells. Further analysis revealed that SIRT3 interacted with and deacetylated the lactate dehydrogenase A (LDHA), a key protein in regulating anaerobic glycolysis, enhancing LDHA activity. In consistence, a cluster of glycolysis-associated genes was upregulated in the SIRT3-overexpressing gastric tumor cells. Thus, in addition to the well-documented SIRT3-mediated mitochondrial homeostasis in normal cells, SIRT3 may enhance glycolysis and cell proliferation in SIRT3-expressing cancer cells.

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-accuracyscreeningapproaches 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.

Effects of the suppression of lactate dehydrogenase A on the growth and invasion of human gastric cancer cells.

Lactate dehydrogenase A (LDH-A), which regulates glycolytic flux by catalyzing pyruvate to lactate in the cytoplasm, is believed to be one of the highly attractive therapeutic targets for cancers. Firstly, we detected the expression of LDH-A in gastric cancer (GC) cells. LDH-A inhibitor oxamate was then used to suppress the LDH-A activity in GC cells. Cell proliferation, lactic acid production, Transwell migration assay and apoptosis were assessed, respectively. The results showed that inhibition of LDH-A by oxamate decreased the lactate production. In the presence of glucose, oxamate inhibited cell proliferation in a dose-dependent manner. Flow cytometry assay further confirmed a pro-apoptotic effect of oxamate, and this was likely through increased expression of Bax, activated caspase-3, and decreased expression of Bcl-2. Therefore, we believe that oxamate inhibits cell growth, suppresses tumor invasion, and induces apoptosis in GC cells. LDH-A may be a potential therapeutic target for GC.

Synthesis, cytotoxicity for mimics of catalase: Inhibitors of lactate dehydrogenase and hypoxia inducible factor

Lactate dehydrogenase A (LDH-A) is a potentially important metabolic target for the inhibition of the highly activated glycolysis pathway in cancer cells. Two Mn(II) complexes with ligand containing di(pyridylmethyl) amine and pyrrol-ketone were used to attenuate the activity of LDH-A. The inhibition of the manganese(II) complexes on the proliferation of HepG-2 cells is related to their ability to disproportionate H2O2. Importantly, the synthesized mimic of catalase can decrease the expression of hypoxia inducible factor (HIF-1α) in HepG-2 cells. So we envision that the multifunctional mimics of catalase could attenuate the activity of LDH-A signaling the cancer cells to death through HIF-1α involved path.

Cetuximab Reverses the Warburg Effect by Inhibiting HIF-1–Regulated LDH-A

Hypoxia-inducible factor-1 (HIF-1) plays a critical role in reprogramming cancer metabolism toward aerobic glycolysis (i.e., the Warburg effect), which is critical to supplying cancer cells with the biomass needed for proliferation. Previous studies have shown that cetuximab, an EGF receptor-blocking monoclonal antibody, downregulates the alpha subunit of HIF-1 (HIF-1α) through the inhibition of EGF receptor downstream cell signaling and that downregulation of HIF-1α is required for cetuximab-induced antiproliferative effects. However, the mechanism underlying these actions has yet to be identified. In this study, we used the Seahorse XF96 extracellular flux analyzer to assess the effect of cetuximab treatment on changes in glycolysis and mitochondrial respiration, the two major energy-producing pathways, in live cells. We found that cetuximab downregulated lactate dehydrogenase A (LDH-A) and inhibited glycolysis in cetuximab-sensitive head and neck squamous cell carcinoma (HNSCC) cells in an HIF-1α downregulation-dependent manner. HNSCC cells with acquired cetuximab resistance expressed a high level of HIF-1α and were highly glycolytic. Overexpression of a HIF-1α mutant (HIF-1α/ΔODD) conferred resistance to cetuximab-induced G1 phase cell-cycle arrest, which could be overcome by knockdown of LDH-A expression. Inhibition of LDH-A activity with oxamate enhanced the response of cetuximab-resistant cells to cetuximab. Cetuximab had no noticeable inhibitory effect on glycolysis in nontransformed cells. These findings provide novel mechanistic insights into cetuximab-induced cell-cycle arrest from the perspective of cancer metabolism and suggest novel strategies for enhancing cetuximab response.

LDH-A Acetylation: Implication in Cancer

LDH-A Acetylation: Implication in Cancer

Abstract 2418: JQ-1, a novel c-Myc inhibitor, suppressed cell proliferation and metabolism through the downregulation of lactate dehydrogenase A in ovarian cancer cells.

Abstract Introduction: Amplification and overexpression of c-Myc is very common in human cancers, including ovarian cancer. Heightened aerobic glycolysis (the Warburg effect) is a key metabolic hallmark of cancer and is thought to be under the control of c-Myc. JQ-1 is a selective small-molecure BET bromodomain inhibitor, and BET inhibition by JQ-1 leads to the downregulation of MYC transcription. Thus, JQ-1 functions as a novel c-Myc inhibitor and has been found to potently suppress tumor growth in hematologic malignancies. Thus, we aim to assess the impact of JQ-1 on the proliferation of human ovarian cancer cell lines and further explore its effects on cellular metabolism, especially the aerobic glycolysis pathway and its key enzyme—lactate dehydrogenase A (LDHA). Methods: Three human ovarian cancer cell lines (HEY and SKOV3) were used in this study. Cell proliferation was assessed by MTT assay after exposure to JQ-1 (generously provided by the laboratory of Dr. James E. Bradner). Cell cycle progression was evaluated by Cellometer. Apoptosis was assessed by Annexin V-FITC assay. Expression of c-Myc, p21, phosphorylated-LDHA and pan-LDHA were detected by Western blot analysis. Cellular glucose uptake, ATP production, reactive oxygen species (ROS), LDHA activity and lactate production were determined by ELISA assay using the corresponding commercial kits. Mitochondrial membrane potential changes were measured by JC-1 staining via Cellometer. Results: JQ-1 suppressed cellular proliferation (IC50 = 360 nM for HEY, p = 0.00001; IC50 = 3500 nM for SKOV3, p = 0.0007) via G1 cell cycle arrest in the ovarian cancer cell lines, but only caused moderate apoptosis. Western blot analysis demonstrated that JQ-1 increased p21 expression and decreased expression of c-Myc and phosphorylation of LDHA. In parallel, treatment with JQ-1 decreased LDHA activity, glucose uptake, mitochondrial membrane potential, lactate and ATP production and increased ROS levels in the ovarian cancer cell lines. Conclusions: We find that targeting c-Myc by JQ-1 significantly suppresses proliferation through G1 arrest in ovarian cancer cell lines. In addition, JQ-1 had multiple influences on cancer metabolism, particularly in the aerobic glycolysis pathway. JQ-1 reduced both the expression and activity of LDHA, inhibited lactate production and decreased the energy supply of the ovarian cancer cells. This evidence suggests that JQ-1 may be a promising targeted therapy for ovarian cancer through its effects on both cell proliferation and metabolism. Citation Format: Haifeng Qiu, Chunxiao Zhou, Amanda L. Jackson, Joshua E. Kilgore, Victoria L. Bae-Jump. JQ-1, a novel c-Myc inhibitor, suppressed cell proliferation and metabolism through the downregulation of lactate dehydrogenase A in ovarian cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2418. doi:10.1158/1538-7445.AM2013-2418

Lysine-5 Acetylation Negatively Regulates Lactate Dehydrogenase A and Is Decreased in Pancreatic Cancer

Tumor cells commonly have increased glucose uptake and lactate accumulation. Lactate is produced from pyruvate by lactate dehydrogenase A (LDH-A), which is frequently overexpressed in tumor cells and is important for cell growth. Elevated transcription by c-Myc or HIF1α may contribute to increased LDH-A in some cancer types. Here, we show that LDH-A is acetylated at lysine 5 (K5) and that this acetylation inhibits LDH-A activity. Furthermore, the K5-acetylated LDH-A is recognized by the HSC70 chaperone and delivered to lysosomes for degradation. Replacement of endogenous LDH-A with an acetylation mimetic mutant decreases cell proliferation and migration. Importantly, K5 acetylation of LDH-A is reduced in human pancreatic cancers. Our study reveals a mechanism of LDH-A upregulation in pancreatic cancers.

Bioactivity-Guided Identification and Cell Signaling Technology to Delineate the Lactate Dehydrogenase A Inhibition Effects of Spatholobus suberectus on Breast Cancer

Aerobic glycolysis is an important feature of cancer cells. In recent years, lactate dehydrogenase A (LDH-A) is emerging as a novel therapeutic target for cancer treatment. Seeking LDH-A inhibitors from natural resources has been paid much attention for drug discovery. Spatholobus suberectus (SS) is a common herbal medicine used in China for treating blood-stasis related diseases such as cancer. This study aims to explore the potential medicinal application of SS for LDH-A inhibition on breast cancer and to determine its bioactive compounds. We found that SS manifested apoptosis-inducing, cell cycle arresting and anti-LDH-A activities in both estrogen-dependent human MCF-7 cells and estrogen-independent MDA-MB-231 cell. Oral herbal extracts (1 g/kg/d) administration attenuated tumor growth and LDH-A expression in both breast cancer xenografts. Bioactivity-guided fractionation finally identified epigallocatechin as a key compound in SS inhibiting LDH-A activity. Further studies revealed that LDH-A plays a critical role in mediating the apoptosis-induction effects of epigallocatechin. The inhibited LDH-A activities by epigallocatechin is attributed to disassociation of Hsp90 from HIF-1α and subsequent accelerated HIF-1α proteasome degradation. In vivo study also demonstrated that epigallocatechin could significantly inhibit breast cancer growth, HIF-1α/LDH-A expression and trigger apoptosis without bringing toxic effects. The preclinical study thus suggests that the potential medicinal application of SS for inhibiting cancer LDH-A activity and the possibility to consider epigallocatechin as a lead compound to develop LDH-A inhibitors. Future studies of SS for chemoprevention or chemosensitization against breast cancer are thus warranted.

Galloflavin prevents the binding of lactate dehydrogenase A to single stranded DNA and inhibits RNA synthesis in cultured cells

Lactate dehydrogenase A (LDH-A) binds single stranded DNA (ssDNA) and stimulates cell transcription. Binding is prevented by NADH, suggesting that the coenzyme site is involved in the interaction LDH-A/ssDNA. We recently identified an inhibitor of LDH-A enzymatic activity (Galloflavin, GF) which occupies the NADH site. In the experiments reported here we studied whether GF can also hinder the binding of LDH-A to ssDNA and investigated its effects on RNA synthesis in cultured cells. Using a filter binding assay we observed that 4μM GF inhibited the binding of human LDH-A to a single stranded [3H]DNA sample by 50%. After only 0.5–1h, 50–100μM GF inhibited RNA synthesis in SW620 cells maintained in a medium in which galactose substituted glucose. In these culture conditions, SW620 cells did not produce lactic acid and effects caused by the inhibition of the enzymatic activity of LDH-A could be excluded.Novel LDH-A inhibitors which hinder aerobic glycolysis of cancer cells are at present actively searched. Our results suggest that: (i) inhibitors which bind the NADH site can exert their antiproliferative activity not only by blocking aerobic glycolysis but also by causing an inhibition of RNA synthesis independent from the effect on glycolysis; (ii) GF can be a useful tool to study the biological role of LDH-A binding to ssDNA.

Antioxidant α-tocopherol checks lymphoma promotion via regulation of expression of protein kinase C-α and c-Myc genes and glycolytic metabolism

Overproduction of reactive oxygen species (ROS) due to environmental challenge or metabolic imbalance leads to oxidative stress, causing overactivation of a number of oncogenes that promote cancer development. Therefore, antioxidants should be able to check cancer growth by modulating oncogene activity. The requirement of high energy during unlimited cell proliferation is fulfilled by the switching of cancerous cells to a fast glycolytic pathway bypassing the oxygen dependent respiratory pathway. Almost all cancers exhibit a high expression of lactate dehydrogenase A (LDH-A) to ensure a high energy supply. The present study focused on modulating redox-sensitive oncogenes such as protein kinase C (PKC) and c-Myc by treatment of lymphoma bearing mice with the antioxidant α-tocopherol, the most active component of vitamin E. Further, the impact of α-tocopherol on LDH activity was tested. The results showed down-regulation of expression of stress-activated genes PKC-α, c-Myc and LDH-A by α-tocopherol in cancerous mice. α-Tocopherol contributes to the check of cell proliferation by decreasing the activity of LDH-A.

Tyrosine Phosphorylation of Lactate Dehydrogenase A Is Important for NADH/NAD+ Redox Homeostasis in Cancer Cells

The Warburg effect describes an increase in aerobic glycolysis and enhanced lactate production in cancer cells. Lactate dehydrogenase A (LDH-A) regulates the last step of glycolysis that generates lactate and permits the regeneration of NAD(+). LDH-A gene expression is believed to be upregulated by both HIF and Myc in cancer cells to achieve increased lactate production. However, how oncogenic signals activate LDH-A to regulate cancer cell metabolism remains unclear. We found that the oncogenic receptor tyrosine kinase FGFR1 directly phosphorylates LDH-A. Phosphorylation at Y10 and Y83 enhances LDH-A activity by enhancing the formation of active, tetrameric LDH-A and the binding of LDH-A substrate NADH, respectively. Moreover, Y10 phosphorylation of LDH-A is common in diverse human cancer cells, which correlates with activation of multiple oncogenic tyrosine kinases. Interestingly, cancer cells with stable knockdown of endogenous LDH-A and rescue expression of a catalytic hypomorph LDH-A mutant, Y10F, demonstrate increased respiration through mitochondrial complex I to sustain glycolysis by providing NAD(+). However, such a compensatory increase in mitochondrial respiration in Y10F cells is insufficient to fully sustain glycolysis. Y10 rescue cells show decreased cell proliferation and ATP levels under hypoxia and reduced tumor growth in xenograft nude mice. Our findings suggest that tyrosine phosphorylation enhances LDH-A enzyme activity to promote the Warburg effect and tumor growth by regulating the NADH/NAD(+) redox homeostasis, representing an acute molecular mechanism underlying the enhanced lactate production in cancer cells.