Identification of N-acylhydrazone derivatives as novel lactate dehydrogenase A inhibitors.

Glycolysis is drastically increased in tumors and it is the main route to energy production with a minor use of oxidative phosphorylation. Among the key enzymes in the glycolytic process, LDH is emerging as one of the most interesting targets for the development of new inhibitors. In this context, in the present work, we carried out a virtual screening procedure followed by chemical modifications of the identified structures according to a "hit-to-lead" process. The effects of the new molecules were preliminary probed against purified human LDH-A. The compounds active at low micromolar level were additionally characterized for their activity on some cellular metabolic processes by using Raji human cell line. Within the series, 1 was considered the best candidate, and a more detailed characterization of its biological properties was performed. In Raji cells exposed to compound 1 we evidenced the occurrence of effects usually observed in cancer cells after LDH-A inhibition: reduced lactate production and NAD/NADH ratio, apoptosis. The flow cytometry analysis of treated cells also showed cell cycle changes compatible with effects exerted at the glycolytic level. Finally, in agreement with the data obtained with other inhibitors or by silencing LDH-A expression, compound 1 was found to increase Raji cells response to some commonly used chemotherapeutic agents. Taken together, all these finding are in support of the LDH-A inhibiting activity of compound 1.

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.

NAD metabolism and functions: a common therapeutic target for neoplastic, metabolic and neurodegenerative diseases.

In recent years the study of nicotinamide adenine dinucleotide (NAD) biochemistry has been the focus of attention for many researchers. Although the role of NAD in cellular metabolism and in redox reactions had been recognized for over a century, it was also during these recent studies that the precise identification of all NAD biosynthetic routes was achieved and that the variety of NAD controlled cellular processes began to emerge. Being vital not only for energy transduction, but also for intracellular signaling pathways, this pyridine nucleotide can be considered the most important link between energetic and regulatory processes. The control of such important events suggested NAD as a possible therapeutic target for the control of different pathological states, including metabolic disorders and neoplastic transformation. This review briefly summarizes the recent advances achieved in this field.

Galloflavin suppresses lactate dehydrogenase activity and causes MYC downregulation in Burkitt lymphoma cells through NAD/NADH-dependent inhibition of sirtuin-1.

Activation of the myc oncogene in cancer cells upregulates lactate dehydrogenase A (LDH-A) expression, leading to a sustained glycolytic flux that is needed to produce ATP under hypoxic conditions. We studied the effects of galloflavin (GF), a recently identified LDH inhibitor, on myc overexpressing Burkitt lymphoma (BL) cells. Epstein-Barr virus-infected lymphoblasts were used as a non-neoplastic control. Our results showed that myc overactivation induced a two- to seven-fold increase in LDH-A expression in BL cells compared with non-neoplastic lymphoblasts; this result is consistent with previously reported data. Moreover, GF treatment suppressed LDH activity and inhibited BL cell replication but did not affect lymphoblast viability. Surprisingly, we found that increased levels of the MYC and LDH-A proteins did not lead to a metabolic shift in BL cells toward glycolytic ATP generation. BL cells were treated with GF at doses that achieved 50% inhibition of cell growth and lactate production, and ATP levels were scarcely affected after GF treatment. The same results were also obtained by suppressing LDH activity with oxamate, an LDH specific inhibitor. Our data suggest that LDH activity is important for maintaining a correct NAD/NADH balance in BL cells. LDH inhibition led to decreased NAD cellular levels, which resulted in sirtuin-1 inhibition. Confirming previous studies, sirtuin-1 inhibition caused a reduction in MYC protein levels, depriving BL cells of their most important survival signal. This study further describes the biological functions of the LDH enzyme and suggests that LDH inhibition could be useful for the treatment of cancer.

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 4 µM GF inhibited the binding of human LDH-A to a single stranded [(3)H]DNA sample by 50%. After only 0.5-1h, 50-100 µM 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.

Galloflavin (CAS 568-80-9): a novel inhibitor of lactate dehydrogenase.

One of the most prominent alterations in cancer cells is their strict dependence on the glycolytic pathway for ATP generation. This observation led to the evaluation of glycolysis inhibitors as potential anticancer agents. The inhibition of lactate dehydrogenase (LDH) is a promising way to inhibit tumor cell glucose metabolism without affecting the energetic balance of normal tissues. However, the success of this approach depends chiefly on the availability of inhibitors that display good selectivity. We identified a compound (galloflavin, CAS 568-80-9) which, in contrast to other inhibitors of human LDH, hinders both the A and B isoforms of the enzyme. To determine the mechanism of action, we collected LDH-A and -B inhibition data in competition reactions with pyruvate or NADH and evaluated the results using software for enzyme kinetics analysis. We found that galloflavin inhibits both human LDH isoforms by preferentially binding the free enzyme, without competing with the substrate or cofactor. The calculated Ki values for pyruvate were 5.46 µM (LDH-A) and 15.06 µM (LDH-B). In cultured tumor cells, galloflavin blocked aerobic glycolysis at micromolar concentrations, did not interfere with cell respiration, and induced cell death by triggering apoptosis. To our knowledge, the inhibition of LDH is, to date, the only biochemical effect described for galloflavin. Because galloflavin is not commercially available, we also describe herein a procedure for its synthesis and report its first full chemical characterization.

Effect of sorafenib on the energy metabolism of hepatocellular carcinoma cells.

Recent data demonstrated that sorafenib impaired the oxidative phosphorylation of a rat myogenic cell line and suggested that this biochemical lesion can contribute to the cardiac toxicity caused by the drug. With the experiments reported here, we verified whether sorafenib inhibits oxidative phosphorylation also in cells from human hepatocellular carcinomas (HCCs), which are treated with this drug. By using the HCC cell lines PLC/PRF/5 and SNU-449 we studied the effects of the drug on ATP cellular levels, oxygen consumption and aerobic glycolysis, a metabolic pathway generally used by neoplastic cells to meet their energy demand. The effect of sorafenib on ATP cellular levels was also studied in cells grown in a glucose-free medium, which only derive their energy from oxidative phosphorylation. We found that at clinically relevant concentrations sorafenib hindered oxidative phosphorylation, whereas at the same time stimulated aerobic glycolysis in glucose-grown cells, thus attenuating the cellular ATP depletion. These results support the impairment of oxidative phosphorylation as a mechanism contributing to the antineoplastic activity of sorafenib in the treatment of HCCs.

Inhibition of lactic dehydrogenase as a way to increase the anti-proliferative effect of multi-targeted kinase inhibitors.

Protein kinase inhibitors are a relatively new class of promising anticancer drugs, most of which exert their action by binding to the ATP site on the targeted kinases. We hypothesized that a decrease in ATP levels in neoplastic cells could reduce the competition for the same enzymatic site, thus increasing the efficacy of kinase inhibitors. Using oxamic acid, an inhibitor of lactic dehydrogenase (LDH) which hinders aerobic glycolysis, we decreased ATP levels in PLC/PRF/5 cells (a line from a hepatocellular carcinoma). We found that in these cells oxamic acid potentiated the antiproliferative activity of sorafenib, imatinib and sunitinib, three kinase inhibitors. When aerobic glycolysis was shut down by culturing the cells in the absence of glucose, oxamic acid did not reduce the ATP levels, suggesting that in normal tissues, which do not rely on aerobic glycolysis for their ATP synthesis, the block of LDH should not impair cellular metabolism. In conclusion, the inhibition of LDH could enhance anticancer activity of sorafenib, imatinib and sunitinib without increasing their side effects on normal cells, which in conditions of normal functional activity and sufficient oxygen supply do not need the activity of this enzyme.

Human RCAN3 gene expression and cell growth in endothelial cells.

Regulator of calcineurin 3 (RCAN3) belongs to the human RCAN gene family, which also includes RCAN1 and RCAN2. All three members interact with and inhibit calcineurin. Based on this effect, several studies have demonstrated a role for RCAN1 and RCAN2 on inflammation, using human umbilical vein endothelial cells (HUVECs) as a model. RCAN1 and 2 are strongly induced by vascular endothelial growth factor (VEGF), inhibit cell proliferation and down-regulate many pro-inflammatory and pro-angiogenic genes. The present work is the first study to investigate the role of RCAN3 on inflammation in HUVECs. RCAN3 isoforms have been characterized and quantified in HUVECs; only those with the same frame are expressed and show a peculiar expression pattern. RCAN3 inhibits HUVEC proliferation both basally and under VEGF or phorbol 12-myristate 13-acetate-stimulated conditions, however it does not modulate gene expression of the chosen inflammatory genes. Results indicate an interesting role for RCAN3 in modulating HUVEC proliferation, independently from the inflammatory and angiogenic processes.

Impairment of aerobic glycolysis by inhibitors of lactic dehydrogenase hinders the growth of human hepatocellular carcinoma cell lines.

BACKGROUND/AIMS: by reducing the number of ATP molecules produced via aerobic glycolysis, the inhibition of lactic dehydrogenase (LDH) should hinder the growth of neoplastic cells without damaging the normal cells which do not rely on this metabolic pathway for their energetic needs. Here, we studied the effect of oxamic and tartronic acids, 2 inhibitors of LDH, on aerobic glycolysis and cell replication of HepG2 and PLC/PRF/5 cells, 2 lines from human hepatocellular carcinomas. METHODS: aerobic glycolysis was measured by calculating the amounts of lactic acid formed. The effect on replication was assessed by culturing the cells in both standard conditions and glucose-deprived medium, which was used to shut down aerobic glycolysis. RESULTS: the oxamic and tartronic acids inhibited aerobic glycolysis, impaired the growth of both cell lines and also induced an increased expression of p53-upregulated modulator of apoptosis, a signal of cell death. A strong impairment of cell replication by oxamic acid was only found when the cells were cultured in the presence of glucose, indicating that it was for the most part owing to inhibition of aerobic glycolysis. CONCLUSIONS: inhibition of aerobic glycolysis achieved by blocking LDH could be useful in the treatment of human hepatocellular carcinomas. Without interfering with glucose metabolism in normal cells, it could hinder cell growth by itself and could also enhance the chemotherapeutic index of associated anticancer agents by decreasing the levels of ATP selectively in neoplastic cells.