Nihed Draoui

Lactate shuttles at a glance: from physiological paradigms to anti-cancer treatments

Hypoxia and oncogene expression both stimulate glycolytic metabolism in tumors, thereby leading to lactate production. However, lactate is more than merely a by-product of glycolysis: it can be used as a metabolic fuel by oxidative cancer cells. This phenomenon resembles processes that have been described for skeletal muscle and brain that involve what are known as cell-cell and intracellular lactate shuttles. Two control points regulate lactate shuttles: the lactate dehydrogenase (LDH)-dependent conversion of lactate into pyruvate (and back), and the transport of lactate into and out of cells through specific monocarboxylate transporters (MCTs). In tumors, MCT4 is largely involved in hypoxia-driven lactate release, whereas the uptake of lactate into both tumor cells and tumor endothelial cells occurs via MCT1. Translating knowledge of lactate shuttles to the cancer field offers new perspectives to therapeutically target the hypoxic tumor microenvironment and to tackle tumor angiogenesis.

Antitumor activity of 7-aminocarboxycoumarin derivatives, a new class of potent inhibitors of lactate influx but not efflux.

High lactate concentration in tumors is associated with bad prognosis. Lactate is released by glycolytic cells in tumors and recaptured by oxidative cancer cells to feed the tricarboxylic acid (TCA) cycle after conversion into pyruvate. Monocarboxylate transporters (MCT) mediate these fluxes of proton-linked lactate and represent attractive targets to interrupt lactate shuttle and to inhibit tumor growth. Here, we investigated the properties of 7-aminocarboxycoumarins (7ACC) developed to selectively interfere with lactate fluxes in the lactate-rich tumor microenvironment. The pharmacologic properties of two compounds of this family, including their effects on lactate influx and efflux and antitumor activity, were investigated using human cancer cell lines and mouse xenograft models. Contrary to the reference MCT1 inhibitor AR-C155858, 7ACC unexpectedly inhibited lactate influx but not efflux in tumor cells expressing MCT1 and MCT4 transporters. 7ACC delayed the growth of cervix SiHa tumors, colorectal HCT116 tumors, and orthoptopic MCF-7 breast tumors. MCT target engagement was confirmed by the lack of activity of 7ACC on bladder UM-UC-3 carcinoma that does not express functional MCT. 7ACC also inhibited SiHa tumor relapse after treatment with cisplatin. Finally, we found that contrary to AR-C155858, 7ACC did not prevent the cell entry of the substrate-mimetic drug 3-bromopyruvate (3BP) through MCT1, and contributed to the inhibition of tumor relapse after 3BP treatment. In conclusion, our results indicate that 7ACC selectively affects a single part of the MCT symporter translocation cycle, leading to strict inhibition of lactate influx. This singular activity is associated with antitumor effects less prone to resistance and side effects. Mol Cancer Ther; 13(6); 1410–8. ©2014 AACR.

The SIRT1/HIF2α Axis Drives Reductive Glutamine Metabolism under Chronic Acidosis and Alters Tumor Response to Therapy

Extracellular tumor acidosis largely results from an exacerbated glycolytic flux in cancer and cancer-associated cells. Conversely, little is known about how tumor cells adapt their metabolism to acidosis. Here, we demonstrate that long-term exposure of cancer cells to acidic pH leads to a metabolic reprogramming toward glutamine metabolism. This switch is triggered by the need to reduce the production of protons from glycolysis and further maintained by the NAD(+)-dependent increase in SIRT1 deacetylase activity to ensure intracellular pH homeostasis. A consecutive increase in HIF2α activity promotes the expression of various transporters and enzymes supporting the reductive and oxidative glutamine metabolism, whereas a reduction in functional HIF1α expression consolidates the inhibition of glycolysis. Finally, in vitro and in vivo experiments document that acidosis accounts for a net increase in tumor sensitivity to inhibitors of SIRT1 and glutaminase GLS1. These findings highlight the influence that tumor acidosis and metabolism exert on each other.

Synthesis and pharmacological evaluation of carboxycoumarins as a new antitumor treatment targeting lactate transport in cancer cells.

Under hypoxia, cancer cells consume glucose and release lactate at a high rate. Lactate was recently documented to be recaptured by oxygenated cancer cells to fuel the TCA cycle and thereby to support tumor growth. Monocarboxylate transporters (MCT) are the main lactate carriers and therefore represent potential therapeutic targets to limit cancer progression. In this study, we have developed and implemented a stepwise in vitro screening procedure on human cancer cells to identify new potent MCT inhibitors. Various 7-substituted carboxycoumarins and quinolinone derivatives were synthesized and pharmacologically evaluated. Most active compounds were obtained using a palladium-catalyzed Buchwald-Hartwig type coupling reaction, which proved to be a quick and efficient method to obtain aminocarboxycoumarin derivatives. Inhibition of lactate flux revealed that the most active compound 19 (IC50 11 nM) was three log orders more active than the CHC reference compound. Comparison with warfarin, a conventional anticoagulant coumarin, further showed that compound 19 did not influence the prothrombin time which, together with a good in vitro ADME profile, supports the potential of this new family of compounds to act as anticancer drugs through inhibition of lactate flux.

Vitamin E-based micelles enhance the anticancer activity of doxorubicin.

The purpose of this study was to develop vitamin E-based micelles loaded with Doxorubicin (DOX) (DOX-TOS-TPGS), taking advantages of the anti-cancer activity of vitamin E derivatives: Tocopherol succinate (TOS) and D-α-tocopherol polyethylene2000 succinate (TPGS). Therefore, we developed micelles consisting in a mixture of TOS (as solubilizer) and TPGS2000 (as stabilizer) (1:1). DOX-TOS-TPGS micelles exhibited a size of 78 nm and a ζ potential of -7 mV. High drug loading (40% w/w) was achieved. The critical micellar concentration was determined at 14 μg/ml. In vitro, after 24 h, DOX-TOS-TPGS micelles exhibited higher cytotoxicity than free-DOX (IC50 on MCF-7 cells, at 24 h, 58 vs 5 μg/ml). In vivo anti-tumor efficacy, performed on two tumor models (CT26 and MCF-7), demonstrated a 100% long-term survival of mice when treated with DOX-TOS-TPGS compared to DOX-free. Interestingly, the survival time of mice treated with unloaded TOS-TPGS micelles was similar to DOX-free, indicating an anti-cancer activity of vitamin E derivatives. Based on these results, it can be concluded that the formulations developed in this work may be considered as an effective DOX delivery system for cancer chemotherapy.

Search for monoglyceride lipase inhibitors: synthesis and screening of arylthioamides derivatives

Monoglyceride lipase (MGL) is the enzyme responsible for the termination of 2-arachidonoylglycerol (2-AG) signalling, an endogenous ligand for the G-protein coupled cannabinoid receptors CB1 and CB2. Its known abundance and physiological roles emphasize the interest of MGL as an attractive therapeutic target. Search for MGL inhibitors was undertaken by screening an arylthioamide series. The evaluation of arylthioamides derivatives activity as MGL inhibitors measured by the hydrolysis of [3H]-2-oleoylglycerol by human purified MGL led to the identification of (2-chloro-phenyl)-morpholin-4-yl-methanethione (2) and (3-nitro-phenyl) morpholin-4-yl-methanethione (12), which moreover exhibit good selectivity compared with human fatty acid amide hydrolase inhibition.

Endothelial cell metabolism: an update anno 2017

Purpose of review Endothelial cell metabolism has recently emerged as an important coregulator of angiogenesis and is therefore a promising new target in various angiogenesis-associated illnesses, like cancer. In this review, we discuss recent insights in endothelial cell metabolism in both physiological and pathological conditions and discuss possible translational implications. Recent findings Two metabolic pathways that determine the performance of endothelial cells are glycolysis and fatty acid oxidation (FAO). Glycolysis is essential as endothelial cells primarily rely on this pathway for ATP production. 6-Phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3) is a key regulator of glycolysis in endothelial cells. As endothelial cells increase glycolysis even further during angiogenesis, PFKFB3 also controls vessel sprouting and promotes endothelial cell migration. Moreover, in tumors, additional PFKFB3 upregulation leads to a more immature and dysfunctional vasculature. PFKFB3 blockade therefore results in tumor vessel normalization, with beneficial therapeutic effects on reduced metastasis and improved chemotherapy. Also, FAO stimulates endothelial cell proliferation through affecting DNA synthesis, and is critical for lymphangiogenesis, in part through epigenetic changes in histone acetylation. As FAO is controlled by carnitine palmitoyltransferase 1a, inhibition of this key enzyme decreases pathological angiogenesis. Summary Both PFKFB3 and carnitine palmitoyltransferase 1a are key metabolic regulators of vessel sprouting and promising new therapeutic targets in diseases associated with pathological angiogenesis.

A new ER-specific photosensitizer unravels (1)O2-driven protein oxidation and inhibition of deubiquitinases as a generic mechanism for cancer PDT.

Photosensitizers (PS) are ideally devoid of any activity in the absence of photoactivation, and rely on molecular oxygen for the formation of singlet oxygen (1O2) to produce cellular damage. Off-targets and tumor hypoxia therefore represent obstacles for the use of PS for cancer photodynamic therapy. Herein, we describe the characterization of OR141, a benzophenazine compound identified through a phenotypic screening for its capacity to be strictly activated by light and to kill a large variety of tumor cells under both normoxia and hypoxia. This new class of PS unraveled an unsuspected common mechanism of action for PS that involves the combined inhibition of the mammalian target of rapamycin (mTOR) signaling pathway and proteasomal deubiquitinases (DUBs) USP14 and UCH37. Oxidation of mTOR and other endoplasmic reticulum (ER)-associated proteins drives the early formation of high molecular weight (MW) complexes of multimeric proteins, the concomitant blockade of DUBs preventing their degradation and precipitating cell death. Furthermore, we validated the antitumor effects of OR141 in vivo and documented its highly selective accumulation in the ER, further increasing the ER stress resulting from 1O2 generation upon light activation.

One-pot synthesis and in vitro antitumor activity of some bipyrazolic tripodal derivatives

The synthesis and structure-activity relationships (SAR) antitumor activities of monopyrazolic and bipyrazolic tripodal derivs. were reported here for the first time. The ten products were tested against three human cancer cell lines including breast (MDA-MB231), prostate (PC3) and colorectal (LoVo) cancers. In bipyrazolic series, most of them exhibited a moderate antitumor activity against three human cancer cell lines with an order of 5 > 7 > 8 in case of colorectal cancer and 5 > 7 ≈ 8 in case of breast and prostate cancers.

Interruption of lactate uptake by inhibiting mitochondrial pyruvate transport unravels direct antitumor and radiosensitizing effects

Lactate exchange between glycolytic and oxidative cancer cells is proposed to optimize tumor growth. Blocking lactate uptake through monocarboxylate transporter 1 (MCT1) represents an attractive therapeutic strategy but may stimulate glucose consumption by oxidative cancer cells. We report here that inhibition of mitochondrial pyruvate carrier (MPC) activity fulfils the tasks of blocking lactate use while preventing glucose oxidative metabolism. Using in vitro 13C-glucose and in vivo hyperpolarized 13C-pyruvate, we identify 7ACC2 as a potent inhibitor of mitochondrial pyruvate transport which consecutively blocks extracellular lactate uptake by promoting intracellular pyruvate accumulation. Also, while in spheroids MCT1 inhibition leads to cytostatic effects, MPC activity inhibition induces cytotoxic effects together with glycolysis stimulation and uncompensated inhibition of mitochondrial respiration. Hypoxia reduction obtained with 7ACC2 is further shown to sensitize tumor xenografts to radiotherapy. This study positions MPC as a control point for lactate metabolism and expands on the anticancer potential of MPC inhibition.Tumor cells can fuel their metabolism with lactate. Here the authors show that inhibition of mitochondrial pyruvate carrier (MPC) blocks extracellular lactate uptake by promoting intracellular pyruvate accumulation and inhibits oxidative metabolism, ultimately resulting in cytotoxicity and radiosensitization.