Biological Activity of Natural and Synthetic Compounds

A drug discovery program starts when a disease or clinical condition has no suitable drugs. In response, the pharmaceutical industry and academic research groups can follow different processes aimed at identifying new molecules with drug-like properties that efficiently modulate the desired biological target. These new chemical entities can be isolated from natural sources or obtained by chemical synthesis, as demonstrated by the articles and review papers reported in this Special Issue

New agents against hypoxic tumours counteracting invasiveness and metabolism

My research activity concerns the design and the synthesis of heterocycles which are intended to act against tumour hypoxia. Unlike healthy cells, which are regularly vascularized, cancer tissues are often characterized by hypoxic regions, due to the rapid and uncontrolled cellular growth and the irregular vascular network. This condition brings to the overexpression of several proteins and, among them, two important novel antitumoural targets, that are lysyl oxidase (LOX) and lactate dehydrogenase A (LDH-A), constituted the main focuses of my research, because they are key enzymes involved in hypoxic tumour growth and invasiveness. In particular, LOX is an enzyme implicated in the remodeling of the extracellular matrix and in the promotion of the metastatic process, so it is deeply involved in the invasive ability of hypoxic tumours. This PhD thesis was aimed to design and synthesize hypoxia-activated nitroaromatic pro-drugs of beta-aminoproprionitrile (BAPN), which is a well-known LOX inhibitor that cannot be developed as a drug due to its many unwanted side effects. These prodrugs should be able to selectively delivery BAPN to hypoxic tumour sites in order to block LOX-induced promotion of invasiveness, reducing systemic side effects. The synthesized molecules were biologically evaluated in LOX inhibition and cell invasion assays, and some compounds proved to be promising LOX inhibitors. As for LDH-A, this enzyme is involved in the peculiar sugar metabolism that occurs in invasive cancers, consisting in a metabolic switch (called the “Warburg effect”) from oxidative phosphorylation to an increased anaerobic glycolysis. LDH-A constitutes a major checkpoint in the switch from aerobic to anaerobic glycolysis, by catalysing the reduction of pyruvate to lactate. The genetic or chemical inhibition of this enzyme proved to counteract tumour growth. Furthermore, LDH-A is also a safe target, causing myoglobinuria only during intense anaerobic exercise in people with an hereditary deficiency of this enzyme. In this PhD project, a new class of LDH-A inhibitors based on COOH-substituted N-hydroxyindole structure (NHIs) was designed and synthesized. Enzymatic assays and cellular-based experiments led to the discovery of new promising and selective inhibitors of LDH-A

Lactate dehydrogenase A inhibition by small molecular entities: steps in the right direction

Direct targeting of energy metabolism to defeat cancer is not a recent strategy. Although quite a few drugs use cellular metabolism for their antitumor effect, no direct inhibitors of energy metabolism have been approved by the FDA. Currently, several inhibitors of lactate dehydrogenase A (LDH-A), a key player in glycolysis, are in development. Earlier, we demonstrated the efficacy of N-hydroxyindole-based LDH-A inhibitors in different cancer types. In this study we describe the efficacy of NHI-Glc-2, which is designed to dual target cancer cells, by exploiting a simultaneous enhanced glucose uptake by overexpressed glucose transporter 1 (GLUT1) and by inhibition of LDH-A. NHI-Glc-2 inhibits LDH-A enzyme activity, PANC-1 cell growth and disrupts spheroid integrity, with an overall effect that is more pronounced when combined with gemcitabine

An update on therapeutic opportunities offered by cancer glycolytic metabolism

AbstractAlmost all invasive cancers, regardless of tissue origin, are characterized by specific modifications of their cellular energy metabolism. In fact, a strong predominance of aerobic glycolysis over oxidative phosphorylation (Warburg effect) is usually associated with aggressive tumour phenotypes. This metabolic shift offers a survival advantage to cancer cells, since they may continue to produce energy and anabolites even when they are exposed to either transient or permanent hypoxic conditions. Moreover, it ensures a high production rate of glycolysis intermediates, useful as building blocks for fast cell proliferation of cancer cells. This peculiar metabolic profile may constitute an ideal target for therapeutic interventions that selectively hit cancer cells with minimal residual systemic toxicity. In this review we provide an update about some of the most recent advances in the discovery of new bioactive molecules that are able to interfere with cancer glycolysis

α/β-Hydrolase Domain (ABHD) Inhibitors as New Potential Therapeutic Options against Lipid-Related Diseases

Much of the experimental evidence in the literature has linked altered lipid metabolism to severe diseases such as cancer, obesity, cardiovascular pathologies, diabetes, and neurodegenerative diseases. Therefore, targeting key effectors of the dysregulated lipid metabolism may represent an effective strategy to counteract these pathological conditions. In this context, α/β-hydrolase domain (ABHD) enzymes represent an important and diversified family of proteins, which are involved in the complex environment of lipid signaling, metabolism, and regulation. Moreover, some members of the ABHD family play an important role in the endocannabinoid system, being designated to terminate the signaling of the key endocannabinoid regulator 2-arachidonoylglycerol. This Perspective summarizes the research progress in the development of ABHD inhibitors and modulators: design strategies, structure-activity relationships, action mechanisms, and biological studies of the main ABHD ligands will be highlighted

Receptor-based virtual screening evaluation for the identification of estrogen receptor β ligands.

In this paper, a receptor-based virtual screening study for the identification of estrogen receptor β (ERβ) ligands was developed. Starting from a commercial database of 400,000 molecules, only six compounds resulted to be potential active ligands of ERβ. Interestingly, all the six molecules possess scaffolds that had already been reported in known ERβ ligands. Therefore, the results obtained herein confirm the reliability of our virtual screening procedure, thus encouraging the application of this protocol to larger commercial databases in order to identify new ERβ ligands

Discovery and optimization of benzoylpiperidine derivatives as new reversible, potent and selective MAGL inhibitors

The serine hydrolase monoacylglycerol lipase (MAGL) is the main responsible of the degradation of 2-arachidonoylglycerol, an endocannabinoid implicated in several physiological processes. Moreover, MAGL is involved in the formation of pro-tumorigenic signaling molecules. MAGL inhibition is considered a valid therapeutic approach to treat several pathological conditions, including several types of cancer.[1] So far, only a limited number of MAGL inhibitors have been discovered and most of them are characterized by an irreversible mechanism of action, determining the occurrence of undesired effects. In this study we identified a reversible MAGL inhibitor by a structure-based virtual screening analysis. With the aim of identifying more potent and selective MAGL inhibitors, chemical modifications were introduced to the original compound to improve both potency and selectivity.[2] The structural optimization led to the obtainment of nanomolar inhibitors (Figure 1), which are selective over other hydrolases and cannabinoid receptors. These new inhibitors exert an appreciable antiproliferative activity in cancer cells and are able to inhibit MAGL in in vivo assays. [1] Mulvihill MM, Nomura DK, Life Sci. 2013; 92(8-9):492-497. [2] Granchi C, Rizzolio F, Palazzolo S, Carmignani S, Macchia M, Saccomanni G, Manera C, Martinelli A, Minutolo F, Tuccinardi T, J Med Chem. 2016; 59(22):10299-10314

Salicylketoximes as inhibitors of Glucose Transporters

Some derivatives of the 4-arylsalicylketoximes series displayed inhibitory effects on glucose transport and on cell proliferation in several biological assays,[1] resulting to be effective GLUT1 inhibitors also in GLUT1-containing giant vesicles. GLUT1 is one of the 14 glucose transporter isoforms, widely overexpressed in many cancer types. Thus, for the discovered properties, the oximes of interest represent interesting candidates for anticancer therapy. Variously substituted 4-arylsalicylketoximes (3, Fig.1) were synthetized via Suzuki cross-coupling and a subsequent condensation of the resulting biaryl-ketone intermediates with hydroxylamine hydrochloride. [1] Rat GLUT1 membrane proteins were produced by Pichia Pastoris cultures, and purified following GLUT1 purification protocols, [2] which were largely revised to avoid the protein cleavage. Compounds 3a, 3b, 3e, and 3f efficiently inhibited glucose uptake in GLUT1-containing giant vesicle assays. [3] To study the nature of the binding process between GLUT1 and the synthetic compounds, many crystallization attempts were set up with 3a and 3e using Lipidic Cubic Phase method, which produced many small crystals. Since many isoforms of GLUTs are overexpressed in cancer cells, inhibition of other GLUT isoforms, such as GLUT3, will be tested in the near future. In conclusion, 4-arylsalicylketoximes showed good inhibition of GLUT1 isoform. First results from GLUT3-giant vesicles assays revealed that, within this series of compounds, 3a is the most selective GLUT1-inhibitor. Further assays with GLUTs-containing giant vesicle and crystallization attempts are currently underway. [1] Granchi C, Qian Y, Lee H.Y, Paterni I, Pasero C, Iegre J, Carlson K. E, Tuccinardi T, Chen X, Katzenellenbogen J. A, Hergenrother P. J, Minutolo F, ChemMedChem. 2015; 1892–1900. [2] Venskutonyté R, Elbing K, Lindkvist-Petersson K, Methods Mol Biol. 2018; 1713, 1–13. [3] Hansen J.H, Elbing K, Thompson J.R, Malmstadt N, Lindkvist-Petersson K, Chem. Commun. 2015; 51, 2316–2319

Natural compounds as inhibitors of lactate dehydrogenase

Lactate dehydrogenase (LDH) catalyses the conversion of pyruvate to lactate, utilizing NADH as co-factor. It’s a tetrameric enzyme composed of two subunits, M and H, whose association can generate five isoforms. One of this, the human isoform 5, hLDH5 has the highest activity in converting pyruvate to lactate under anaerobic conditions, such as those found in hypoxic tumors and for this reason it’s up-regulated in tumor tissues where cells glycolytic rate is up to 200 times higher than that of the normal tissue. hLDH5 inhibition should cause cancer cell death by starvation, without interfering with healthy cells that normally use oxidative phosphorylation for ATP generation (1). Inhibition of LDH is so considered as a promising target in cancer treatment, and natural compounds could serve as useful scaffold to study new anticancer agents. Among the few plant derived hLDH5 inhibitors already investigated there are mainly phenolic derivatives such as gossypol, morin, and galloflavin (2,3). In the last decade our research group successfully detected a good number of compounds obtained from Mediterranean plants with anticancer effect, and for this reason start a research program aimed to discover new classes of natural products having hLDH5 inhibitory activity. In a first study, since some species of Phlomis (Lamiaceae) proved to possess anti-cancer properties, the crude extract of P. kurdica aerial parts was selected as the starting material. Two new flavonoids and one new phenylpropanoid, together with eleven known phenolic compounds, including flavonoids and phenylpropanoids were isolated and assayed for their hLDH5 inhibitory activity. Luteolin 7-O-β-D-glucopyranoside showed an IC50 value similar to that of reference compound galloflavin (4). Then, since Polygala genus (Polygalaceae) is well known to contain phenolic oligosaccharides, xanthones, lignans, and triterpenic saponins and it’s largely used in the traditional medicine, an Italian species P. flavescens subsp. flavescens was chosen. Ten new compounds were isolated from the methanol residue of the aerial parts through Sephadex and RP-HPLC separations, including four flavonol glycosides, two oligosaccharides, one α-ionone, and three triterpenoidic saponins, together with two known oligosaccharides and two flavonol glycosides. The isolates were assayed for their inhibitory activity against hLDH5 and 3,6'-di-O-sinapoylsucrose showed an inhibition potency comparable or even slightly better than reference inhibitor galloflavin. Docking studies were carried out to hypothesize the interaction mode of active compounds in the enzyme active site

Identification of Lactate Dehydrogenase 5 Inhibitors using Pharmacophore- Driven Consensus Docking

Background: Human lactate dehydrogenase 5 (hLDH5) represents a promising anticancer target, particularly for the treatment of hypoxic tumors, where it is often hyperexpressed. In fact, by catalyzing the reduction of pyruvate to lactate, hLDH5 allows the survival of tumor cells under hypoxic conditions by means of glycolysis. Despite the efforts dedicated to the identification and development of hLDH5 inhibitors, only few compounds showing promising activity in cancer cell lines have been reported. Objective: In the present study, we developed a virtual screening (VS) protocol aimed at identifying new small molecule inhibitors of hLDH5. Method: The VS strategy consisted in a pharmacophore-driven consensus docking (CD) approach, combining a structure-based pharmacophore screening and CD protocol employing three different docking methods. Results: The VS protocol was applied to filter the Enamine commercial database and allowed the selection of three candidate ligands to be subjected to hLDH5 inhibition assays. One of the selected compounds showed a promising activity, compared to its low molecular weight, with an IC50 of 180.7 ± 16.5 μM. Conclusion: We identified a new small-molecule inhibitor of hLDH5 that can be considered as a new lead for the development of potent hLDH5 inhibitors. Moreover, these results demonstrate the reliability of the VS protocol developed