Anticancer agents interacting with membrane glucose transporters.

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

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

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

Synergistic interaction of novel lactate dehydrogenase inhibitors with gemcitabine against pancreatic cancer cells in hypoxia.

BACKGROUND: Hypoxia is a driving force in pancreatic-ductal-adenocarcinoma (PDAC) growth, metastasis and chemoresistance. The muscle-isoform of lactate dehydrogenase (LDH-A) constitutes a major checkpoint for the switch to anaerobic glycolysis, ensuring supply of energy and anabolites in hypoxic-environments. Therefore, we investigated the molecular mechanisms underlying the pharmacological interaction of novel LDH-A inhibitors in combination with gemcitabine in PDAC cells. METHODS: Lactate dehydrogenase A levels were studied by quantitative RT-PCR, western blot, immunofluorescence and activity assays in 14 PDAC cells, including primary-cell-cultures and spheroids, in normoxic and hypoxic conditions. Cell proliferation, migration and key determinants of drug activity were evaluated by sulforhodamine-B-assay, wound-healing assay, PCR and LC-MS/MS. RESULTS: Lactate dehydrogenase A was significantly increased under hypoxic conditions (1% O2), where the novel LDH-A inhibitors proved to be particularly effective (e.g., with IC50 values of 0.9 vs 16.3 µM for NHI-1 in LPC006 in hypoxia vs normoxia, respectively). These compounds induced apoptosis, affected invasiveness and spheroid-growth, reducing expression of metalloproteinases and cancer-stem-like-cells markers (CD133+). Their synergistic interaction with gemcitabine, with combination index values <0.4 in hypoxia, might also be attributed to modulation of gemcitabine metabolism, overcoming the reduced synthesis of phosphorylated metabolites. CONCLUSION: Lactate dehydrogenase A is a viable target in PDAC, and novel LDH-A inhibitors display synergistic cytotoxic activity with gemcitabine, offering an innovative tool in hypoxic tumours.

Inhibitors of lactate dehydrogenase isoforms and their therapeutic potentials.

In many different species, lactate dehydrogenase (LDH) constitutes a major checkpoint of anaerobic glycolysis, by catalyzing the reduction of pyruvate into lactate. This enzyme has recently received a great deal of attention since it may constitute a valid therapeutic target for diseases so different as malaria and cancer. In fact, the isoform expressed by Plasmodium falciparum (pfLDH) is a key enzyme for energy generation of malarial parasites. These species mostly depend on anaerobic glycolysis for energy production, since they lack a citric acid cycle for ATP formation. Therefore, inhibitors of pfLDH would potentially cause mortality of P. falciparum and, to this purpose, several small organic molecules have been recently designed and developed with the aim of blocking this new potential antimalarial chemotherapeutic target. Moreover, most invasive tumour phenotypes show a metabolic switch (Warburg effect) from oxidative phosphorylation to an increased anaerobic glycolysis, by promoting an upregulation of the human isoform-5 of lactate dehydrogenase (hLDH-5 or LDH-A), which is normally present in muscles and in the liver. Hence, inhibition of hLDH-5 may constitute an efficient way to interfere with tumour growth and invasiveness. This review provides an overview of the LDH inhibitors that have been developed up to now, an analysis of their possible isoform-selectivity, and their therapeutic potentials.