New Hybrid Compounds Incorporating Natural Products as Multifunctional Agents against Alzheimer's Disease

A series of new hybrid derivatives 1a-c, 2a-c, 3a-c, 4a-c, 5a-c, inspired by nature, were synthesized and studied as multifunctional agents for the treatment of Alzheimer's disease (AD). These compounds were designed to merge together the trifluoromethyl benzyloxyaminic bioactive moiety, previously identified, with different acids available in nature. The ability of the synthesized compounds to chelate biometals, such as Cu2+, Zn2+ and Fe2+, was studied by UV-Vis spectrometer, and through a preliminary screening their antioxidant activity was evaluated by DPPH. Then, selected compounds were tested by in vitro ABTS free radical method and ex vivo rat brain TBARS assay. Compounds 2a-c, combining the strongest antioxidant and biometal chelators activities, were studied for their ability to contrast Aβ1-40 fibrillization process. Finally, starting from the promising profile obtained for compound 2a, we evaluated if it could be able to induce a positive cross-interaction between transthyretin (TTR) and Aβ in presence and in absence of Cu2+.

Pomegranate: A Source of Multifunctional Bioactive Compounds Potentially Beneficial in Alzheimer's Disease

Pomegranate fruit (PF) is a fruit rich in nutraceuticals. Nonedible parts of the fruit, especially peels, contain high amounts of bioactive components that have been largely used in traditional medicine, such as the Chinese, Unani, and Ayurvedic ones, for treating several diseases. Polyphenols such as anthocyanins, tannins, flavonoids, phenolic acids, and lignans are the major bioactive molecules present in PF. Therefore, PF is considered a source of natural multifunctional agents that exert simultaneously antioxidant, anti-inflammatory, antitumor, antidiabetic, cardiovascular, and neuroprotective activities. Recently, several studies have reported that the nutraceuticals contained in PF (seed, peel, and juice) have a potential beneficial role in Alzheimer's disease (AD). Research suggests that the neuroprotective effect of PF is mostly due to its potent antioxidant and anti-inflammatory activities which contribute to attenuate the neuroinflammation associated with AD. Despite the numerous works conducted on PF, to date the mechanism by which PF acts in combatting AD is not completely known. Here, we summarize all the recent findings (in vitro and in vivo studies) related to the positive effects that PF and its bioactive components can have in the neurodegeneration processes occurring during AD. Moreover, considering the high biotransformation characteristics of the nutraceuticals present in PF, we propose to consider the chemical structure of its active metabolites as a source of inspiration to design new molecules with the same beneficial effects but less prone to be affected by the metabolic degradation process.

Identification of N-Acyl Hydrazones as New Non-Zinc-Binding MMP-13 Inhibitors by Structure-Based Virtual Screening Studies and Chemical Optimization

Matrix metalloproteinase 13 plays a central role in osteoarthritis (OA), as its overexpression induces an excessive breakdown of collagen that results in an imbalance between collagen synthesis and degradation in the joint, leading to progressive articular cartilage degradation. Therefore, MMP-13 has been proposed as a key therapeutic target for OA. Here we have developed a virtual screening workflow aimed at identifying selective non-zinc-binding MMP-13 inhibitors by targeting the deep S1' pocket of MMP-13. Three ligands were found to inhibit MMP-13 in the µM range, and one of these showed selectivity over other MMPs. A structure-based analysis guided the chemical optimization of the hit compound, leading to the obtaining of a new N-acyl hydrazone-based derivative with improved inhibitory activity and selectivity for the target enzyme.

Resveratrol-like Compounds as SIRT1 Activators

The sirtuin 1 (SIRT1) activator resveratrol has emerged as a promising candidate for the prevention of vascular oxidative stress, which is a trigger for endothelial dysfunction. However, its clinical use is limited by low oral bioavailability. In this work, we have applied a previously developed computational protocol to identify the most promising derivatives from our in-house chemical library of resveratrol derivatives. The most promising compounds in terms of SIRT1 activation and oral bioavailability, predicted in silico, were evaluated for their ability to activate the isolated SIRT1 enzyme. Then, we assessed the antioxidant effects of the most effective derivative, compound 3d, in human umbilical vein endothelial cells (HUVECs) injured with H₂O₂ 100 µM. The SIRT1 activator 3d significantly preserved cell viability and prevented an intracellular reactive oxygen species increase in HUVECs exposed to the oxidative stimulus. Such effects were partially reduced in the presence of a sirtuin inhibitor, sirtinol, confirming the potential role of sirtuins in the activity of resveratrol and its derivatives. Although 3d appeared less effective than resveratrol in activating the isolated enzyme, the effects exhibited by both compounds in HUVECs were almost superimposable, suggesting a higher ability of 3d to cross cell membranes and activate the intracellular target SIRT1.

Pterostilbene fluorescent probes as potential tools for targeting neurodegeneration in biological applications

Several epidemiological studies suggest that a diet rich in fruit and vegetables reduces the incidence of neurodegenerative diseases. Resveratrol (Res) and its dimethylated metabolite, pterostibene (Ptb), have been largely studied for their neuroprotective action. The clinical use of Res is limited because of its rapid metabolism and its poor bioavailability. Ptb with two methoxy groups and one hydroxyl group has a good membrane permeability, metabolic stability and higher in vivo bioavailability in comparison with Res. The metabolism and pharmacokinetics of Ptb are still sparse, probably due to the lack of tools that allow following the Ptb destiny both in living cells and in vivo. In this contest, we propose two Ptb fluorescent derivatives where Ptb has been functionalised by benzofurazan and rhodamine-B-isothiocyanate, compounds 1 and 2, respectively. Here, we report the synthesis, the optical and structural characterisation of 1 and 2, and, their putative cytotoxicity in two different cell lines.

Nature-Inspired O-Benzyl Oxime-Based Derivatives as New Dual-Acting Agents Targeting Aldose Reductase and Oxidative Stress

Aldose reductase (ALR2) is the enzyme in charge of developing cellular toxicity caused by diabetic hyperglycemia, which in turn leads to the generation of reactive oxygen species triggering oxidative stress. Therefore, inhibiting ALR2 while pursuing a concomitant anti-oxidant activity through dual-acting agents is now recognized as the gold standard treatment for preventing or at least delaying the progression of diabetic complications. Herein we describe a novel series of (E)-benzaldehyde O-benzyl oximes 6a–e, 7a–e, 8a–e, and 9–11 as ALR2 inhibitors endowed with anti-oxidant properties. Inspired by the natural products, the synthesized derivatives are characterized by a different polyhydroxy substitution pattern on their benzaldehyde fragment, which proved crucial for both the enzyme inhibitory activity and the anti-oxidant capacity. Derivatives (E)-2,3,4-trihydroxybenzaldehyde O-(3-methoxybenzyl) oxime (7b) and (E)-2,3,4-trihydroxybenzaldehyde O-(4-methoxybenzyl) oxime (8b) turned out to be the most effective dual-acting products, proving to combine the best ALR2 inhibitory properties with significant anti-oxidant efficacy.

Multifunctional Small Molecules as Potential Anti-Alzheimer's Disease Agents

Alzheimer's disease (AD) is a severe multifactorial neurodegenerative disorder characterized by a progressive loss of neurons in the brain. Despite research efforts, the pathogenesis and mechanism of AD progression are not yet completely understood. There are only a few symptomatic drugs approved for the treatment of AD. The multifactorial character of AD suggests that it is important to develop molecules able to target the numerous pathological mechanisms associated with the disease. Thus, in the context of the worldwide recognized interest of multifunctional ligand therapy, we report herein the synthesis, characterization, physicochemical and biological evaluation of a set of five (1a-e) new ferulic acid-based hybrid compounds, namely feroyl-benzyloxyamidic derivatives enclosing different substituent groups, as potential anti-Alzheimer's disease agents. These hybrids can keep both the radical scavenging activity and metal chelation capacity of the naturally occurring ferulic acid scaffold, presenting also good/mild capacity for inhibition of self-Aβ aggregation and fairly good inhibition of Cu-induced Aβ aggregation. The predicted pharmacokinetic properties point towards good absorption, comparable to known oral drugs.

Activation of carbonic anhydrases from human brain by amino alcohol oxime ethers: towards human carbonic anhydrase VII selective activators

The synthesis and carbonic anhydrase (CA; EC 4.2.1.1) activating effects of a series of oxime ether-based amino alcohols towards four human (h) CA isoforms expressed in human brain, hCA I, II, IV and VII, are described. Most investigated amino alcohol derivatives induced a consistent activation of the tested CAs, with K_As spanning from a low micromolar to a medium nanomolar range. Specifically, hCA II and VII, putative main CA targets when central nervous system (CNS) diseases are concerned, were most efficiently activated by these oxime ether derivatives. Furthermore, a multitude of selective hCA VII activators were identified. As hCA VII is one of the key isoforms involved in brain metabolism and other brain functions, the identified potent and selective hCA VII activators may be considered of interest for investigations of various therapeutic applications or as lead compounds in search of even more potent and selective CA activators.

Identification of histone deacetylase inhibitors with (arylidene)aminoxy scaffold active in uveal melanoma cell lines

Uveal melanoma (UM) represents an aggressive type of cancer and currently, there is no effective treatment for this metastatic disease. In the last years, histone deacetylase inhibitors (HDACIs) have been studied as a possible therapeutic treatment for UM, alone or in association with other chemotherapeutic agents. Here we synthesised a series of new HDACIs based on the SAHA scaffold bearing an (arylidene)aminoxy moiety. Their HDAC inhibitory activity was evaluated on isolated human HDAC1, 3, 6, and 8 by fluorometric assay and their binding mode in the catalytic site of HDACs was studied by molecular docking. The most promising hit was the quinoline derivative VS13, a nanomolar inhibitor of HDAC6, which exhibited a good antiproliferative effect on UM cell lines at micromolar concentration and a capability to modify the mRNA levels of HDAC target genes similar to that of SAHA.

Oxy-imino saccharidic derivatives as a new structural class of aldose reductase inhibitors endowed with anti-oxidant activity

Aldose reductase is a key enzyme in the development of long term diabetic complications and its inhibition represents a viable therapeutic solution for people affected by these pathologies. Therefore, the search for effective aldose reductase inhibitors is a timely and pressing challenge. Herein we describe the access to a novel class of oxyimino derivatives, obtained by reaction of a 1,5-dicarbonyl substrate with O-(arylmethyl)hydroxylamines. The synthesised compounds proved to be active against the target enzyme. The best performing inhibitor, compound (Z)-8, proved also to reduce both cell death and the apoptotic process when tested in an in vitro model of diabetic retinopathy made of photoreceptor-like 661w cell line exposed to high-glucose medium, counteracting oxidative stress triggered by hyperglycaemic conditions.

Natural Marine and Terrestrial Compounds as Modulators of Matrix Metalloproteinases-2 (MMP-2) and MMP-9 in Alzheimer's Disease

Several studies have reported neuroprotective effects by natural products. A wide range of natural compounds have been investigated, and some of these may play a beneficial role in Alzheimer's disease (AD) progression. Matrix metalloproteinases (MMPs), a family of zinc-dependent endopeptidases, have been implicated in AD. In particular, MMP-2 and MMP-9 are able to trigger several neuroinflammatory and neurodegenerative pathways. In this review, we summarize and discuss existing literature on natural marine and terrestrial compounds, as well as their ability to modulate MMP-2 and MMP-9, and we evaluate their potential as therapeutic compounds for neurodegenerative and neuroinflammatory diseases, with a focus on Alzheimer's disease.

Neuroglobin and neuroprotection: the role of natural and synthetic compounds in neuroglobin pharmacological induction

Neuroglobin (Ngb) is a 17 kDa monomeric hexa-coordinated heme protein belonging to the globin family. Ngb is mainly expressed in neurons of the central and peripheral nervous system, although moderate levels of Ngb have been detected in non-nervous tissues. In the past decade, Ngb has been studied for its neuroprotective role in a large number of neurological disorders such as Alzheimer's disease, Huntington's disease, brain ischemia and hypoxia. This review discusses and summarizes the natural compounds and the small synthetic molecules capable of modulating Ngb expression that exhibits a protective role against various neurodegenerative diseases.

Natural compounds as inhibitors of transthyretin amyloidosis and neuroprotective agents: analysis of structural data for future drug design

Natural compounds, such as plant and fruit extracts have shown neuroprotective effect against neurodegenerative diseases. It has been reported that several natural compounds binding to transthyretin (TTR) can be useful in amyloidosis prevention. TTR is a transporter protein that under physiological condition carries thyroxine (T4) and retinol in plasma and in cerebrospinal fluid (CSF); it also has a neuroprotective role against Alzheimer's disease (AD). However, TTR also is an amyloidogenic protein responsible for familial amyloid polyneuropathy (FAP) and familial amyloid cardiomyopathy (FAC). The TTR amyloidogenic potential is speeded up by several point mutations. One therapeutic strategy against TTR amyloidosis is the stabilisation of the native tetramer by natural compounds and small molecules. In this review, we examine the natural products that, starting from 2012 to present, have been studied as a stabiliser of TTR tetramer. In particular, we discussed the chemical and structural features which will be helpful for future drug design of new TTR stabilisers.

Focus on Human Monoamine Transporter Selectivity. New Human DAT and NET Models, Experimental Validation, and SERT Affinity Exploration

The most commonly used antidepressant drugs are the serotonin transporter inhibitors. Their effects depend strongly on the selectivity for a single monoamine transporter compared to other amine transporters or receptors, and the selectivity is roughly influenced by the spatial protein structure. Here, we provide a computational study on three human monoamine transporters, i.e., DAT, NET, and SERT. Starting from the construction of hDAT and hNET models, whose three-dimensional structure is unknown, and the prediction of the binding pose for 19 known inhibitors, 3D-QSAR models of three human transporters were built. The training set variability, which was high in structure and activity profile, was validated using a set of in-house compounds. Results concern more than one aspect. First of all, hDAT and hNET three-dimensional structures were built, validated, and compared to the hSERT one; second, the computational study highlighted the differences in binding site arrangement statistically correlated to inhibitor selectivity; third, the profiling of new inhibitors pointed out a conservation of the inhibitory activity trend between rabbit and human SERT with a difference of about 1 order of magnitude; fourth, binding and functional studies confirmed 4-(benzyloxy)-4-phenylpiperidine 20a–d and 21a–d as potent SERT inhibitors. In particular, one of the compounds (compound 20b) revealed a higher affinity for SERT than paroxetine in human platelets.

Age-related Macular Degeneration: Current Knowledge of Zinc Metalloproteinases Involvement

BACKGROUND

Advanced age-related macular degeneration (AMD) is the leading cause of blindness in the elderly with limited therapeutic options. The disease is characterized by photoreceptor loss in the macula and reduced Retinal Pigment Epithelium (RPE) function, associated with matrix degradation, cell proliferation, neovascularization and inflammation. Matrix metalloproteinases (MMPs), a disintegrin and metalloproteinases (ADAMs) and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTSs) play a critical role in the physiology of extracellular matrix (ECM) turnover and, in turn, in ECM pathologies, such as AMD. A balance between the activities of MMPs and Tissue Inhibitors of Metalloproteinase (TIMPs) is crucial for the integrity of the ECM components; indeed, a dysregulation in the ratio of these factors produces profound changes in the ECM, including thickening and deposit formation, which eventually might lead to AMD development.

OBJECTIVE

This article reviews the relevance and impact of zinc metalloproteinases on the development of AMD and their roles as biomarkers and/or therapeutic targets. We illustrate some studies on several inhibitors of MMPs currently used to dissect physiological properties of MMPs. Moreover, all molecules or technologies used to control MMP and ADAM activity in AMD are analyzed.

CONCLUSION

This study underlines the changes in the activity of MMPs expressed by RPE cells, highlights the functions of already used MMP inhibitors and consequently suggests their application as therapeutic agents for the treatment of AMD.

Design and Synthesis of Ionic Liquid-Based Matrix Metalloproteinase Inhibitors (MMPIs): A Simple Approach to Increase Hydrophilicity and to Develop MMPI-Coated Gold Nanoparticles

Selective and potent matrix metalloproteinase 12 (MMP-12) inhibitors endowed with improved hydrophilicity are highly sought for potential use in the treatment of lung and cardiovascular diseases. In the present paper, we modified the structure of a nanomolar MMP-12 inhibitor by incorporating an ionic liquid (IL) moiety to improve aqueous solubility. Four biologically active salts were obtained by linking the sulfonamide moiety of the MMP-12 inhibitor to imidazolium-, pyrrolidinium-, piperidinium-, and DABCO-based ILs. The imidazolium-based bioactive salt was tested on human recombinant MMPs and on monocyte-derived dendritic cells, showing activity similar to that of the parent compound, but improved water solubility. The imidazolium-based bioactive salt was then used to prepare electrostatically stabilized MMP inhibitor-coated gold nanoparticles (AuNPs) able to selectively bind MMP-12. These AuNPs were used to study subcellular localization of MMP-12 in monocyte-derived dendritic cells by transmission electron microscopy analysis.

Design, synthesis and biological evaluation of bifunctional inhibitors of membrane type 1 matrix metalloproteinase (MT1-MMP)

Collagen degradation and proMMP-2 activation are major functions of MT1-MMP to promote cancer cell invasion. Since both processes require MT1-MMP homodimerization on the cell surface, herein we propose that the use of bifunctional inhibitors of this enzyme could represent an innovative approach to efficiently reduce tumor growth. A small series of symmetrical dimers derived from previously described monomeric arylsulfonamide hydroxamates was synthesized and tested in vitro on isolated MMPs. A nanomolar MT1-MMP inhibitor, compound 6, was identified and then submitted to cell-based assays on HT1080 fibrosarcoma cells. Dimer 6 reduced MT1-MMP-dependent proMMP-2 activation, collagen degradation and collagen invasion in a dose-dependent manner with better results even compared to its monomeric analogue 4. This preliminary study suggests that dimeric MT1-MMP inhibitors might be further developed and exploited as an alternative tool to reduce cancer cell invasion.

Copper mediated amyloid-β binding to Transthyretin

Transthyretin (TTR), a homotetrameric protein that transports thyroxine and retinol both in plasma and in cerebrospinal (CSF) fluid provides a natural protective response against Alzheimer's disease (AD), modulates amyloid-β (Aβ) deposition by direct interaction and co-localizes with Aβ in plaques. TTR levels are lower in the CSF of AD patients. Zn²⁺, Mn²⁺ and Fe²⁺ transform TTR into a protease able to cleave Aβ. To explain these activities, monomer dissociation or conformational changes have been suggested. Here, we report that when TTR crystals are exposed to copper or iron salts, the tetramer undergoes a significant conformational change that alters the dimer-dimer interface and rearranges residues implicated in TTR's ability to neutralize Aβ. We also describe the conformational changes in TTR upon the binding of the various metal ions. Furthermore, using bio-layer interferometry (BLI) with immobilized Aβ(1-28), we observe the binding of TTR only in the presence of copper. Such Cu²⁺-dependent binding suggests a recognition mechanism whereby Cu²⁺ modulates both the TTR conformation, induces a complementary Aβ structure and may participate in the interaction. Cu²⁺-soaked TTR crystals show a conformation different from that induced by Fe²⁺, and intriguingly, TTR crystals grown in presence of Aβ(1-28) show different positions for the copper sites from those grown its absence.

Synthesis and antiangiogenic activity study of new hop chalcone Xanthohumol analogues

Angiogenesis induction is a hallmark of cancer. Antiangiogenic properties of Xanthohumol (XN), a naturally occurring prenylated chalcone from hops, have been widely reported. Here we describe the synthesis and study the antiangiogenic activity in vitro of a series of XN derivatives, where different substituents on the B-ring of the chalcone scaffold were inserted. The new XN derivatives inhibited human umbilical-vein endothelial cell (HUVEC) proliferation, adhesion, migration, invasion and their ability to form capillary-like structures in vitro at 10 μM concentration. The preliminary results indicate that the phenolic OH group in R, present in natural XN, is not necessary for having antiangiogenic activity. In fact, the most effective compound from this series, 13, was characterized by a para-methoxy group in R and a fluorine atom in R₂ on B-ring. This study paves the way for future development of synthetic analogues of XN to be used as cancer angiopreventive and chemopreventive agents.

Bifunctional Inhibitors as a New Tool To Reduce Cancer Cell Invasion by Impairing MMP-9 Homodimerization

Protein homodimers play important roles in physiological and pathological processes, including cancer invasion and metastasis. Recently, MMP-9 natural homodimerization via the PEX domain has been correlated with high migration rates of aggressive cancer cells. Here we propose that bifunctional MMP-9 inhibitors designed to impair natural MMP-9 homodimerization promoted by PEX-PEX interactions might be an effective tool to fight cancer cell invasion. Elaborating a previously described dimeric hydroxamate inhibitor 1, new ligands were synthesized with different linker lengths and branch points. Evaluation of the modified bifunctional ligands by X-ray crystallography and biological assays showed that 7 and 8 could reduce invasion in three glioma cell lines expressing MMP-9 at different levels. To rationalize these results, we present a theoretical model of full-length MMP-9 in complex with 7. This pioneering study suggests that a new approach using MMP-9 selective bifunctional inhibitors might lead to an effective therapy to reduce cancer cell invasion.

Comparison of helical scan and standard rotation methods in single-crystal X-ray data collection strategies

X-ray radiation in macromolecular crystallography can chemically alter the biological material and deteriorate the integrity of the crystal lattice with concomitant loss of resolution. Typical alterations include decarboxylation of glutamic and aspartic residues, breaking of disulfide bonds and the reduction of metal centres. Helical scans add a small translation to the crystal in the rotation method, so that for every image the crystal is shifted to expose a fresh part. On beamline PROXIMA 2A at Synchrotron SOLEIL, this procedure has been tested with various parameters in an attempt to understand how to mitigate the effects of radiation damage. Here, the strategies used and the crystallographic metrics for various scenarios are reported. Among these, the loss of bromine from bromophenyl moieties appears to be a useful monitor of radiation damage as the carbon-bromine bond is very sensitive to X-ray irradiation. Two cases are focused on where helical scans are shown to be superior in obtaining meaningful data compared with conventional methods. In one case the initial resolution of the crystal is extended over time, and in the second case the anomalous signal is preserved to provide greater effective multiplicity and easier phasing.

Targeting Different Transthyretin Binding Sites with Unusual Natural Compounds

Misfolding and aggregation of the transthyretin (TTR) protein leads to certain forms of amyloidosis. Some nutraceuticals, such as flavonoids and natural polyphenols, have recently been investigated as modulators of the self-assembly process of TTR, but they generally suffer from limited bioavailability. To discover innovative and more bioavailable natural compounds able to inhibit TTR amyloid formation, a docking study was performed using the crystallographic structure of TTR. This computational strategy was projected as an ad hoc inspection of the possible relationship between binding site location and modulation of the assembly process; interactions with the as-yet-unexplored epigallocatechin gallate (EGCG) sites and with the thyroxine (T4) pocket were simultaneously analyzed. All the compounds studied seem to prefer the traditional T4 binding site, but some interesting results emerged from the screening of an in-house database, used for validating the computational protocol, and of the Herbal Ingredients Targets (HIT) catalogue available on the ZINC database.

Synthesis and structural analysis of halogen substituted fibril formation inhibitors of Human Transthyretin (TTR)

Transthyretin (TTR), a β-sheet-rich tetrameric protein, in equilibrium with an unstable amyloidogenic monomeric form is responsible for extracellular deposition of amyloid fibrils, is associated with the onset of neurodegenerative diseases, such as senile systemic amyloidosis, familial amyloid polyneuropathy and familial amyloid cardiomyopathy. One of the therapeutic strategies is to use small molecules to stabilize the TTR tetramer and thus curb amyloid fibril formation. Here, we report the synthesis, the in vitro evaluation of several halogen substituted 9-fluorenyl- and di-benzophenon-based ligands and their three-dimensional crystallographic analysis in complex with TTR. The synthesized compounds bind TTR and stabilize the tetramer with different potency. Of these compounds, 2c is the best inhibitor. The dual binding mode prevalent in the absence of substitutions on the fluorenyl ring, is disfavored by (2,7-dichloro-fluoren-9-ylideneaminooxy)-acetic acid (1b), (2,7-dibromo-fluoren-9-ylideneaminooxy)-acetic acid (1c) and (E/Z)-((3,4-dichloro-phenyl)-methyleneaminooxy)-acetic acid (2c), all with halogen substitutions.

A new crystal form of human transthyretin obtained with a curcumin derived ligand

Transthyretin (TTR), a 54kDa homotetrameric protein that transports thyroxine (T4), has been associated with clinical cases of TTR amyloidosis for its tendency to aggregate to form fibrils. Many ligands with a potential to inhibit fibril formation have been studied by X-ray crystallography in complex with TTR. Unfortunately, the ligand is often found in ambiguous electron density that is difficult to interpret. The ligand validation statistics suggest over-interpretation, even for the most active compounds like diflunisal. The primary technical reason is its position on a crystallographic 2-fold axis in the most common crystal form. Further investigations with the use of polyethylene glycol (PEG) to crystallize TTR complexes have resulted in a new trigonal polymorph with two tetramers in the asymmetric unit. The ligand used to obtain this new polymorph, 4-hydroxychalcone, is related to curcumin. Here we evaluate this crystal form to understand the contribution it may bring to the study of TTR ligands complexes, which are often asymmetric.

X-ray crystal structure and activity of fluorenyl-based compounds as transthyretin fibrillogenesis inhibitors

Transthyretin (TTR) is a 54 kDa homotetrameric protein that transports thyroxine (T4) and retinol (vitamin A), through its association with retinol binding protein (RBP). Under unknown conditions, it aggregates to form fibrils associated with TTR amyloidosis. Ligands able to inhibit fibril formation have been studied by X-ray crystallography. The use of polyethylene glycol (PEG) instead of ammonium sulphate or citrate has been evaluated as an alternative to obtain new TTR complexes with (R)-3-(9-fluoren-9-ylideneaminooxy)-2-methyl-N-(methylsulfonyl) propionamide (48R(1)) and 2-(9H-fluoren-9-ylideneaminooxy) acetic acid (ES8(2)). The previously described fluorenyl based inhibitors (S)-3-((9H-fluoren-9-ylideneamino)oxy)-2-methylpropanoic acid (6BD) and 3-((9H-fluoren-9-ylideneamino)oxy)propanoic acid (7BD) have been re-evaluated with the changed crystallization method. The new TTR complexes with compounds of the same family show that the 9-fluorenyl motif can occupy alternative hydrophobic binding sites. This augments the potential use of this scaffold to yield a large variety of differently substituted mono-aryl compounds able to inhibit TTR fibril formation.

Tafamidis (Vyndaqel): a light for FAP patients

Slowing FAP progression: Tafamidis meglumine is a small molecule capable of stabilizing the transthyretin (TTR) tetramer. Tafamidis acts in a similar way to the natural hormone T4, prevents TTR amyloid fibril formation, and offers a potential alternative to liver transplantation for the treatment of patients with TTR familial amyloid polyneuropathies (TTR-FAP).

Arylsulfonamide inhibitors of aggrecanases as potential therapeutic agents for osteoarthritis: synthesis and biological evaluation

Aggrecanases, in particular aggrecanase-2 (ADAMTS-5), are considered the principal proteases responsible for aggrecan degradation in osteoarthritis. For this reason, considerable effort has been put on the discovery and development of aggrecanase inhibitors able to slow down or halt the progression of osteoarthritis. We report herein the synthesis and biological evaluation of a series of arylsulfonamido-based hydroxamates as aggrecanase inhibitors. Compound 18 was found to have a nanomolar activity for ADAMTS-5, ADAMTS-4 and MMP-13 and high selectivity over MMP-1 and MMP-14. Furthermore, this compound proved to be effective in blocking ex vivo cartilage degradation without having effect on cell cytotoxicity.

Tricyclic sulfonamides incorporating benzothiopyrano[4,3-c]pyrazole and pyridothiopyrano[4,3-c]pyrazole effectively inhibit α- and β-carbonic anhydrase: X-ray crystallography and solution investigations on 15 isoforms

Carbonic anhydrases (CAs, EC 4.2.1.1) are ubiquitous isozymes involved in crucial physiological and pathological events, representing the targets of inhibitors with several therapeutic applications. In this connection, we report a new class of carbonic anhydrase inhibitors, based on the thiopyrano-fused pyrazole scaffold to which a pendant 4-sulfamoylphenyl moiety was attached. The new sulfonamides 3a-e were designed as constrained analogues of celecoxib and valdecoxib. The most interesting feature of sulfonamides 3 was their predominantly strong inhibition of human (h) CA I and II, as well as those of the mycobacterial β-class enzymes (Rv1284, Rv3273, and Rv3588c), whereas their inhibitory action against hCA III, IV, VA, VB, VI, VII, IX, XII, XIII, and XIV was found to be at least 2 orders of magnitude lower. X-ray crystallography and structural superposition studies made it possible to explain the very distinct inhibition profile of the tricyclic sulfonamides, different from those of celecoxib and valdecoxib.

TTR fibril formation inhibitors: is there a SAR?

Transthyretin is a homotetrameric protein that carries thyroxine and retinol binding protein in plasma and is associated with a variety of amyloid diseases. One approach to the potential treatment of TTR amyloidosis is the stabilization of the native tetramer, over the dissociative transition state, through the binding of small molecules; this increases the kinetic barrier for tetramer dissociation and prevents protein misfolding. Several molecules discovered through focused screening, or created utilizing the structure-based design, were studied to identify the structural features that could make up for a good candidate drug. In this review, we examine several different chemical classes of TTR fibril formation inhibitors, highlighting the structural modifications that have led to an improvement or to a decrease of their potency and/or selectivity.

A new D₂ dopamine receptor agonist allosterically modulates A(2A) adenosine receptor signalling by interacting with the A(2A)/D₂ receptor heteromer

The structural and functional interaction between D₂ dopamine receptor (DR) and A(2A) adenosine receptor (AR) has suggested these two receptors as a pharmacological target in pathologies associated with dopamine dysfunction, such as Parkinson's disease. In transfected cell lines it has been demonstrated the activation of D₂DR induces a significant negative regulation of A(2A)AR-mediated responses, whereas few data are at now available about the regulation of A(2A)AR by D₂DR agonists at receptor recognition site. In this work we confirmed that in A(2A)AR/D₂DR co-transfected cells, these receptors exist as homo- and hetero-dimers. The classical D₂DR agonists were able to negatively modulate both A(2A)AR affinity and functionality. These effects occurred even if any significant changes in A(2A)AR/D₂DR energy transfer interaction could be detected in BRET experiments. Since the development of new molecules able to target A(2A)/D₂ dimers may represent an attractive tool for innovative pharmacological therapy, we also identified a new small molecule, 3-(3,4-dimethylphenyl)-1-(2-piperidin-1-yl)ethyl)piperidine (compound 1), full agonist of D₂DR and modulator of A(2A)-D₂ receptor dimer. This compound was able to negatively modulate A(2A)AR binding properties and functional responsiveness in a manner comparable to classical D₂R agonists. In contrast to classical agonists, compound 1 led to conformational changes in the quaternary structure in D₂DR homomers and heteromers and induced A(2A)AR/D₂DR co-internalization. These results suggest that compound 1 exerts a high control of the function of heteromers and could represent a starting point for the development of new drugs targeting A(2A)AR/D₂ DR heteromers.

3-[(aryl)(4-fluorobenzyloxy)methyl]piperidine derivatives: high-affinity ligands for the serotonin transporter

The structural requirements for high-affinity binding at the serotonin transporter (SERT) have been investigated through the preparation of some 3-[(aryl)(4-fluorobenzyloxy)methyl]piperidine derivatives. The affinity of synthesised piperidinic compounds (1–4) at the SERT was evaluated by displacement of [3H]-paroxetine binding. Derived inhibition constant (Ki) values were in the same order of magnitude as that of fluoxetine, ranging between 2 and 400 nm. To better define the profiles of these compounds as potential antidepressants, binding affinity for 5-HT1A receptors and α2-adrenoceptors was also investigated by competition experiments using [3H]8-hydroxy-2-(dipropylamino)tetralin ([3H]8-OH-DPAT) and [3H]rauwolscine as radiolabelled ligands, respectively. Inhibition data indicate that compounds 1–4 possess a very weak affinity for these receptors. The high affinity of compound 1 for SERT indicates that it is worth investigating further.

Synthesis and in-vitro antitumour activity of new naphthyridine derivatives on human pancreatic cancer cells

Objectives

The aim of the study was to evaluate the antitumour effect in vitro of newly synthesized 7-substituted 2,3-dihydro-1,8-naphthyridines.

Methods

Characterization tools included cell viability assay, caspase 3/7 induction, DNA fragmentation, fibroblast growth factor type 1 receptor kinase inhibition, and in-vitro antiangiogenic analysis.

Key findings

Treatment of MIA PaCa-2 human pancreatic cancer cells with test compounds showed time- and concentration-dependent cytotoxicity with IC50 values in the micromolar range. Compounds with an aminoalkyl or a diaminoalkyl side chain at the 7-position exhibited remarkable cytotoxicity, whereas the presence of a methyl group or a cyclic amine in the same position led to a significant decrease in their biological activity. Cytotoxicity screening demonstrated that the most active was compound 11 (mean 50% inhibition of cell proliferation (IC50) 11 μM). This compound had an in-vitro antitumour efficacy superior to 5-fluorouracil (the lowest cell viability value after treatment (Emax) 0.2% and 19%, respectively) and proved to be less toxic than 5-fluorouracil against non-cancerous human oral epithelial cells. In addition, compound 11 induced apoptosis in MIA PaCa-2 cells and it was able to promote antiangiogenic effects in vitro. Finally, its cytotoxicity was enhanced in pancreatic cancer cells stimulated with fibroblast growth factor, while no substantial effect was observed on human bronchial smooth muscle cells stimulated with the same growth factor.

Conclusions

These findings suggest that 1,8-naphthyridine derivatives are a promising class of compounds in cancer research. In particular, the antitumour activity of compound 11 is worth further investigation.

Design, synthesis, biological evaluation, and NMR studies of a new series of arylsulfones as selective and potent matrix metalloproteinase-12 inhibitors

Overexpression of macrophage elastase (MMP-12), a member of the matrix metalloproteinases family, can be linked to tissue remodeling and degradation in some inflammatory processes, such as chronic obstructive pulmonary disease (COPD), emphysema, rheumatoid arthritis (RA), and atherosclerosis. On this basis, MMP-12 can be considered an attractive target for studying selective inhibitors that are useful in the development of new therapies for COPD and other inflammatory diseases. We report herein the design, synthesis, and in vitro evaluation of a new series of compounds, possessing an arylsulfonyl scaffold, for their potential as selective inhibitors of MMP-12. The best compound in the series showed an IC50 value of 0.2 nM, with good selectivity over MMP-1 and MMP-14. A docking study was carried out on this compound in order to investigate its binding interactions with MMP-12, and NMR studies on the complex with the MMP-12 catalytic domain were able to validate the proposed binding mode.

N-O-isopropyl sulfonamido-based hydroxamates: design, synthesis and biological evaluation of selective matrix metalloproteinase-13 inhibitors as potential therapeutic agents for osteoarthritis

Matrix metalloproteinase-13 (MMP-13) is a key enzyme implicated in the degradation of the extracellular matrix in osteoarthritis (OA). For this reason, MMP-13 synthetic inhibitors are being sought as potential therapeutic agents to prevent cartilage degradation and to halt the progression of OA. Herein, we report the synthesis and in vitro evaluation of a new series of selective MMP-13 inhibitors possessing an arylsulfonamidic scaffold. Among these potential inhibitors, a very promising compound was discovered exhibiting nanomolar activity for MMP-13 and was highly selective for this enzyme compared to MMP-1, -14, and TACE. This compound acted as a slow-binding inhibitor of MMP-13 and was demonstrated to be effective in an in vitro collagen assay and in a model of cartilage degradation. Furthermore, a docking study was conducted for this compound in order to investigate its binding interactions with MMP-13 and the reasons for its selectivity toward MMP-13 versus other MMPs.

Synthesis and in-vitro antitumour activity of new naphthyridine derivatives on human pancreatic cancer cells

OBJECTIVES

The aim of the study was to evaluate the antitumour effect in vitro of newly synthesized 7-substituted 2,3-dihydro-1,8-naphthyridines.

METHODS

Characterization tools included cell viability assay, caspase 3/7 induction, DNA fragmentation, fibroblast growth factor type 1 receptor kinase inhibition, and in-vitro antiangiogenic analysis.

KEY FINDINGS

Treatment of MIA PaCa-2 human pancreatic cancer cells with test compounds showed time- and concentration-dependent cytotoxicity with IC50 values in the micromolar range. Compounds with an aminoalkyl or a diaminoalkyl side chain at the 7-position exhibited remarkable cytotoxicity, whereas the presence of a methyl group or a cyclic amine in the same position led to a significant decrease in their biological activity. Cytotoxicity screening demonstrated that the most active was compound 11 (mean 50% inhibition of cell proliferation (IC50) 11 mum). This compound had an in-vitro antitumour efficacy superior to 5-fluorouracil (the lowest cell viability value after treatment (E(max)) 0.2% and 19%, respectively) and proved to be less toxic than 5-fluorouracil against non-cancerous human oral epithelial cells. In addition, compound 11 induced apoptosis in MIA PaCa-2 cells and it was able to promote antiangiogenic effects in vitro. Finally, its cytotoxicity was enhanced in pancreatic cancer cells stimulated with fibroblast growth factor, while no substantial effect was observed on human bronchial smooth muscle cells stimulated with the same growth factor.

CONCLUSIONS

These findings suggest that 1,8-naphthyridine derivatives are a promising class of compounds in cancer research. In particular, the antitumour activity of compound 11 is worth further investigation.

Novel transthyretin amyloid fibril formation inhibitors: synthesis, biological evaluation, and X-ray structural analysis

Transthyretin (TTR) is one of thirty non-homologous proteins whose misfolding, dissociation, aggregation, and deposition is linked to human amyloid diseases. Previous studies have identified that TTR amyloidogenesis can be inhibited through stabilization of the native tetramer state by small molecule binding to the thyroid hormone sites of TTR. We have evaluated a new series of β-aminoxypropionic acids (compounds 5–21), with a single aromatic moiety (aryl or fluorenyl) linked through a flexible oxime tether to a carboxylic acid. These compounds are structurally distinct from the native ligand thyroxine and typical halogenated biaryl NSAID-like inhibitors to avoid off-target hormonal or anti-inflammatory activity. Based on an in vitro fibril formation assay, five of these compounds showed significant inhibition of TTR amyloidogenesis, with two fluorenyl compounds displaying inhibitor efficacy comparable to the well-known TTR inhibitor diflunisal. Fluorenyl 15 is the most potent compound in this series and importantly does not show off-target anti-inflammatory activity. Crystal structures of the TTR∶inhibitor complexes, in agreement with molecular docking studies, revealed that the aromatic moiety, linked to the sp²-hybridized oxime carbon, specifically directed the ligand in either a forward or reverse binding mode. Compared to the aryl family members, the bulkier fluorenyl analogs achieved more extensive interactions with the binding pockets of TTR and demonstrated better inhibitory activity in the fibril formation assay. Preliminary optimization efforts are described that focused on replacement of the C-terminal acid in both the aryl and fluorenyl series (compounds 22–32). The compounds presented here constitute a new class of TTR inhibitors that may hold promise in treating amyloid diseases associated with TTR misfolding.

Synthesis and 5-HT2A, 5-HT1A and alpha1-binding affinities of 2-[2-Hydroxy-3-(pyridin-3-yl-methyl)amino]-, 2-[2-hydroxy-3-(2-pyridin-2-yl-ethyl)amino]- and 2-[2-hydroxy-3-(4-N-methyl-piperazin-1-yl)-amino]propoxybenzaldehyde-O-(substituted) benzyl oximes

Some oxime ether-substituted aryloxypropanolamines 3-5, structurally related to the active metabolite 2 of sarpogrelate 1, were synthesized and tested for their affinities at 5-HT2A and 5-HT1A serotoninergic receptors as well as at the alpha1-adrenoceptor. The results show that the compounds possess, at least partially, the ability of the model compounds 1 and 2 to interact with the 5-HT2A-receptors; they have the same selectivity towards 5-HT2A receptors vs alpha1-adrenoceptors.

Carbonic anhydrase and matrix metalloproteinase inhibitors. Inhibition of human tumor-associated isozymes IX and cytosolic isozyme I and II with sulfonylated hydroxamates

A series of sulfonylated hydroxamates were synthesized and evaluated as dual inhibitors of both human carbonic anhydrases (hCAs) and matrix metalloproteinases (MMPs), two metalloenzyme families involved in carcinogenesis and tumor invasion processes. The new derivatives were tested on three CA isozymes, the cytosolic isozymes I and II, and the transmembrane, tumor-associated isozyme IX, and also on human gelatinases (MMP-2 and MMP-9). Some of the new derivatives proved to be potent and selective inhibitors of CA II, but only compounds 3b and 6b, devoid of the arylsulfonyl moiety, proved to have a better inhibitory activity on hCA IX than on hCA I and II, in the micromolar range.

N-i-Propoxy-N-biphenylsulfonylaminobutylhydroxamic acids as potent and selective inhibitors of MMP-2 and MT1-MMP

Structural manipulation of the pharmacophoric model of type A selective MMP inhibitors (MMPi), obtained by the insertion of some alkyl substituents R2 possessing an appropriate geometry, steric bulkiness and lipophilicity, is able to improve potency, in the subnanomolar range on MMP-2, and to give a good MMP inhibition on MMP-14 (MT1-MMP) in the designed MMPi of type C, while maintaining a good MMP-1/MMP-2 selectivity profile. The simultaneous inhibition of these two enzymes yields type C compounds, which are potent antiangiogenic agents, able to block a chemoinvasion model on HUVEC cells in the micromolar range.