Targeting Lewy body dementia with neflamapimod-rasagiline hybrids.

Lewy body dementia (LBD) represents the second most common neurodegenerative dementia but is a quite underexplored therapeutic area. Nepflamapimod (1) is a brain-penetrant selective inhibitor of the alpha isoform of the mitogen-activated serine/threonine protein kinase (MAPK) p38α, recently repurposed for LBD due to its remarkable antineuroinflammatory properties. Neuroprotective propargylamines are another class of molecules with a therapeutical potential against LBD. Herein, we sought to combine the antineuroinflammatory core of 1 and the neuroprotective propargylamine moiety into a single molecule. Particularly, we inserted a propargylamine moiety in position 4 of the 2,6-dichlorophenyl ring of 1, generating neflamapimod-propargylamine hybrids 3 and 4. These hybrids were evaluated using several cell models, aiming to recapitulate the complexity of LBD pathology through different molecular mechanisms. The N-methyl-N-propargyl derivative 4 showed a nanomolar p38α-MAPK inhibitory activity (IC50 = 98.7 nM), which is only 2.6-fold lower compared to that of the parent compound 1, while displaying no hepato- and neurotoxicity up to 25 µM concentration. It also retained a similar immunomodulatory profile against the N9 microglial cell line. Gratifyingly, at 5 µM concentration, 4 demonstrated a neuroprotective effect against dexamethasone-induced reactive oxygen species production in neuronal cells that was higher than that of 1.

From combinations to multitarget-directed ligands: A continuum in Alzheimer's disease polypharmacology.

The continued drug discovery failures in complex neurodegenerative diseases, including Alzheimer's disease (AD), has raised questions about the classical paradigm "one-drug, one-target, one-disease." In parallel, the ever-increasing awareness of the multiplicity of the underlying pathways has led to the affirmation of polypharmacological approaches. Polypharmacology, which broadly embodies the use of pharmaceutical agents acting on multiple targets, seems to be the best way to restore the complex diseased network and to provide disease-modifying effects in AD. In this review, our aim is to provide a roadmap into a world that is still only partly explored and that should be seen as a continuum of pharmacological opportunities, from drug combinations to multitarget-directed ligands (both codrugs and hybrids). Each modality has unique features that can be effectively exploited by medicinal chemists. We argue that understanding their advantages and drawbacks is very helpful in choosing a proper approach and developing successful AD multitarget drug-discovery endeavors. We also briefly dwell on (co)target validation, an aspect that is quite often neglected, but critical for an efficient clinical translation. We substantiate our discussion with instructive examples taken from the recent literature. Our wish is that, in spite of the specter of the high attrition rates, best researchers preferring to enter, stay, and progress in the field would help grow the sector and develop AD polypharmacology to full potential.

Histone deacetylases as targets for the treatment of neurodegenerative disorders: Challenges and future opportunities.

Despite the applicability of histone deacetylase inhibitors (HDACis) for cancer treatment, several works in the literature have shown that these inhibitors can be used in several other diseases, such as neurodegenerative diseases (NDs). This review begins by discussing the signaling pathways of HDACs, focused on the context of NDs, presenting a discussion about the pharmacophoric features of HDACis and crystal structure analysis and discussing interesting case studies from the literature about the development of HDACis. Additionally, a discussion about the consequences of isoform-selective inhibition vs pan-HDACis on neurotoxic effects and clinical trial investigations of HDACis for NDs is also presented. Finally, we describe our perspective related to the future use of these inhibitors in the pharmacotherapy of NDs.

Stereocontrolled transformations of cyclohexadienone derivatives to access stereochemically rich and natural product-inspired architectures.

The last two decades or so have witnessed an upsurge in defining the art of designing complex natural products and nature-inspired molecules. Throughout these decades, fundamental insights into stereocontrolled, step-economic and atom-economical synthesis principles were achieved by the numerous synthetic accomplishments particularly in diversity-oriented synthesis (DOS). This has empowered the visualization of the third dimension in synthetic design and thus has resulted in a dramatic increase with today's diversity-oriented synthesis (DOS) at the forefront enabling access to diverse scaffolds with a high degree of stereochemical and skeletal complexity. To this end, a starting material-based approach is one of the powerful tools utilized in DOS that allows rapid access to molecular architectures with a high sp3 content. Skeletal and stereochemical diversity is often paramount for the selective modulation of the biological function of a complementary protein in the biological space. In this context, stereocontrolled transformation of cyclohexadienone scaffolds has positioned itself as a powerful platform for the rapid generation of stereochemically enriched and natural product-inspired compound collections. In this review, we cover multidirectional synthetic strategies that utilized cyclohexadienone derivatives as pluripotent building blocks en route for the construction of novel chemical space.

Molecular Hybridization as a Tool for Designing Multitarget Drug Candidates for Complex Diseases.

Molecular hybridization is a well-exploited medicinal chemistry strategy that aims to combine two molecules (or parts of them) in a new, single chemical entity. Recently, it has been recognized as an effective approach to design ligands able to modulate multiple targets of interest. Hybrid compounds can be obtained by linking (presence of a linker) or framework integration (merging or fusing) strategies. Although very promising to combat the multifactorial nature of complex diseases, the development of molecular hybrids faces the critical issues of selecting the right target combination and the achievement of a balanced activity towards them, while maintaining drug-like-properties. In this review, we present recent case histories from our own research group that demonstrate why and how molecular hybridization can be carried out to address the challenges of multitarget drug discovery in two therapeutic areas that are Alzheimer's and parasitic diseases. Selected examples spanning from linker- to fragment- based hybrids will allow to discuss issues and consequences relevant to drug design.

Tacrine-O-protected phenolics heterodimers as multitarget-directed ligands against Alzheimer's disease: Selective subnanomolar BuChE inhibitors.

Concerned by the devastating effects of Alzheimer's disease, and the lack of effective drugs, we have carried out the design of a series of tacrine-phenolic heterodimers in order to tackle the multifactorial nature of the disease. Hybridization of both pharmacophores involved the modification of the nature (imino, amino, ether) and the length of the tether, together with the type (hydroxy, methoxy, benzyloxy), number and position of the substituents on the aromatic residue. Title compounds were found to be strong and selective inhibitors of human BuChE (from low nanomolar to subnanomolar range), an enzyme that becomes crucial in the more advanced stages of the disease. The lead compound, bearing an ether-type tether, had an IC50 value of 0.52 nM against human BuChE, and a selectivity index of 323, with an 85-fold increase of activity compared to parent tacrine; key interactions were analysed using molecular modelling. Moreover, it also inhibited the self-aggregation of Aß42, lacking neurotoxicity up to 5 µM concentration, and showed neuroprotective activity in primary rat neurons in a serum and K+ deprivation model, widely employed for reproducing neuronal injury and senescence. Moreover, low hepatoxicity effects and complete stability under physiological conditions were found for that compound. So, overall, our lead compound can be considered as a promising multitarget-directed ligand against Alzheimer's disease, and a good candidate for developing new drugs.

The Mu.Ta.Lig. Chemotheca: A Community-Populated Molecular Database for Multi-Target Ligands Identification and Compound-Repurposing.

For every lead compound developed in medicinal chemistry research, numerous other inactive or less active candidates are synthetized/isolated and tested. The majority of these compounds will not be selected for further development due to a sub-optimal pharmacological profile. However, some poorly active or even inactive compounds could live a second life if tested against other targets. Thus, new therapeutic opportunities could emerge and synergistic activities could be identified and exploited for existing compounds by sharing information between researchers who are working on different targets. The Mu.Ta.Lig (Multi-Target Ligand) Chemotheca database aims to offer such opportunities by facilitating information exchange among researchers worldwide. After a preliminary registration, users can (a) virtually upload structures and activity data for their compounds with corresponding, and eventually known activity data, and (b) search for other available compounds uploaded by the users community. Each piece of information about given compounds is owned by the user who initially uploaded it and multiple ownership is possible (this occurs if different users uploaded the same compounds or information pertaining to the same compounds). A web-based graphical user interface has been developed to assist compound uploading, compounds searching and data retrieval. Physico-chemical and ADME properties as well as substructure-based PAINS evaluations are computed on the fly for each uploaded compound. Samples of compounds that match a set of search criteria and additional data on these compounds could be requested directly from their owners with no mediation by the Mu.Ta.Lig Chemotheca team. Guest access provides a simplified search interface to retrieve only basic information such as compound IDs and related 2D or 3D chemical structures. Moreover, some compounds can be hidden to Guest users according to an owner's decision. In contrast, registered users have full access to all of the Chemotheca data including the permission to upload new compounds and/or update experimental/theoretical data (e.g., activities against new targets tested) related to already stored compounds. In order to facilitate scientific collaborations, all available data are connected to the corresponding owner's email address (available for registered users only). The Chemotheca web site is accessible at http://chemotheca.unicz.it.

Nutritional and Pharmacological Strategies to Regulate Microglial Polarization in Cognitive Aging and Alzheimer's Disease.

The study of microglia, the immune cells of the brain, has experienced a renaissance after the discovery of microglia polarization. In fact, the concept that activated microglia can shift into the M1 pro-inflammatory or M2 neuroprotective phenotypes, depending on brain microenvironment, has completely changed the understanding of microglia in brain aging and neurodegenerative diseases. Microglia polarization is particularly important in aging since an increased inflammatory status of body compartments, including the brain, has been reported in elderly people. In addition, inflammatory markers, mainly derived from activated microglia, are widely present in neurodegenerative diseases. Microglial inflammatory dysfunction, also linked to microglial senescence, has been extensively demonstrated and associated with cognitive impairment in neuropathological conditions related to aging. In fact, microglia polarization is known to influence cognitive function and has therefore become a main player in neurodegenerative diseases leading to dementia. As the life span of human beings increases, so does the prevalence of cognitive dysfunction. Thus, therapeutic strategies aimed to modify microglia polarization are currently being developed. Pharmacological approaches able to shift microglia from M1 pro-inflammatory to M2 neuroprotective phenotype are actually being studied, by acting on many different molecular targets, such as glycogen synthase kinase-3 (GSK3) ß, AMP-activated protein kinase (AMPK), histone deacetylases (HDACs), etc. Furthermore, nutritional approaches can also modify microglia polarization and, consequently, impact cognitive function. Several bioactive compounds normally present in foods, such as polyphenols, can have anti-inflammatory effects on microglia. Both pharmacological and nutritional approaches seem to be promising, but still need further development. Here we review recent data on these approaches and propose that their combination could have a synergistic effect to counteract cognitive aging impairment and Alzheimer's disease (AD) through immunomodulation of microglia polarization, i.e., by driving the shift of activated microglia from the pro-inflammatory M1 to the neuroprotective M2 phenotype.

New tacrine dimers with antioxidant linkers as dual drugs: Anti-Alzheimer's and antiproliferative agents.

We have designed a series of tacrine-based homo- and heterodimers that incorporate an antioxidant tether (selenoureido, chalcogenide) as new dual compounds: for the treatment of Alzheimer's disease and as antiproliferative agents. Symmetrical homodimers bearing a dichalcogenide or selenide-based tether, the best compounds in the series, were found to be strong and highly selective electric eel AChE inhibitors, with inhibition constants within the low nanomolar range. This high inhibitory activity was confirmed on recombinant human AChE for the most interesting derivatives. The three most promising homodimers also showed a good inhibitory activity towards amyloid-ß self aggregation. The symmetric disulfide derivative bis[5-(1',2',3',4'-tetrahydroacridin-9'-ylamino)pentyl]disulfide (19) showed the best multipotent profile and was not neurotoxic on immortalized mouse cortical neurons even at 50 µM concentration. These results represent an improvement in activity and selectivity compared to parent tacrine, the first marketed drug against Alzheimer's disease. Title compounds also exhibited excellent in vitro antiproliferative activities against a panel of 6 human tumor cell lines, with GI50 values within the submicromolar range for the most potent derivatives (0.12-0.95 µM); such values represent a spectacular increase compared to currently-used chemotherapeutic agents, such as 5-FU (up to 306-fold) and cisplatin (up to 162-fold). Cell cycle experiments indicated the accumulation of cells in the G1 phase of the cycle, a different mechanism than the reported for cisplatin. The breast cancer cell lines turned out to be the most sensitive one of the panel tested.

Lipoic acid, a lead structure for multi-target-directed drugs for neurodegeneration.

Nowadays, drug discovery based on a single-target-directed strategy seems inappropriate for the treatment of complex diseases that have multiple pathogenic factors. Recent research into new drugs, which are able to hit different targets, highlights the idea that a single molecule could be sufficient to treat multi-factorial diseases. In this review, examples of multi-target-directed compounds derived from lipoic acid are examined.

Rational approach to discover multipotent anti-Alzheimer drugs.

The coupling of two different pharmacophores, each endowed with different biological properties, afforded the hybrid compound lipocrine (7), whose biological profile was markedly improved relative to those of prototypes tacrine and lipoic acid. Lipocrine is the first compound that inhibits the catalytic activity of AChE and AChE-induced amyloid-beta aggregation and protects against reactive oxygen species. Thus, it emerged as a valuable pharmacological tool to investigate Alzheimer's disease and as a promising lead compound for new anti-Alzheimer drugs.

Presynaptic M3 muscarinic cholinoceptors mediate inhibition of excitatory synaptic transmission in area CA1 of rat hippocampus.

Acetylcholine can modulate hippocampal network function through activation of both nicotinic and muscarinic acetylcholine receptors (mAChRs). All five mAChR subtypes have been identified in the hippocampus. Besides by their involvement in excitability of hippocampal cells, synaptic plasticity and memory, a large body of research has demonstrated the involvement of presynaptic mAChRs in the inhibition of glutamatergic transmission in the hippocampus. Over the years, however, pharmacological and molecular genetic studies have yielded quite contradictory results regarding the mAChR subtype(s) involved. In this study, multi-electrode array technology was used for the pharmacological elucidation of the subtype of mAChR mediating the depression of excitatory synaptic transmission at the SC-CA1 synapse. Using selective antagonists (VU0255035, MT7, tripinamide, MT3) and allosteric potentiators (VU 10010, VU 0238429) the involvement of M1, M2, M4, and M5 subtypes was ruled out thereby implying a major modulatory role for M3 receptors in the inhibition of excitatory synaptic transmission in area CA1 of rat hippocampus.

3,4-Dihydro-1,3,5-triazin-2(1H)-ones as the First Dual BACE-1/GSK-3ß Fragment Hits against Alzheimer's Disease.

One of the main obstacles toward the discovery of effective anti-Alzheimer drugs is the multifactorial nature of its etiopathology. Therefore, the use of multitarget-directed ligands has emerged as particularly suitable. Such ligands, able to modulate different neurodegenerative pathways, for example, amyloid and tau cascades, as well as cognitive and neurogenic functions, are fostered to come. In this respect, we report herein on the first class of BACE-1/GSK-3ß dual inhibitors based on a 3,4-dihydro-1,3,5-triazin-2(1H)-one skeleton, whose hit compound 1 showed interesting properties in a preliminary investigation. Notably, compound 2, endowed with well-balanced potencies against the two isolated enzymes (IC50 of 16 and 7 µM against BACE-1 and GSK-3ß, respectively), displayed effective neuroprotective and neurogenic activities and no neurotoxicity in cell-based assays. It also showed good brain permeability in a pharmacokinetic assessment in mice. Overall, triazinone derivatives, thanks to the simultaneous modulation of multiple points of the diseased network, might emerge as suitable candidates to be tested in in vivo Alzheimer's disease models.

Structure-activity relationships of methoctramine-related polyamines as muscular nicotinic receptor noncompetitive antagonists. 2. Role of polymethylene chain lengths separating amine functions and of substituents on the terminal nitrogen atoms.

Polymethylene tetraamine methoctramine (1) is a prototypical antimuscarinic ligand endowed with a significant affinity for muscular nAChRs. Thus, according to the universal template approach, structural modifications were performed on 1 in order to improve affinity and selectivity for the muscle-type nAChR. The polyamine derivatives synthesized were tested at both frog rectus and Torpedo nAChRs and at guinea pig left atria (M(2)) and ileum longitudinal muscle (M(3)) mAChRs. All of the compounds, like prototype 1, were noncompetitive antagonists of nicotinic receptors while being competitive antagonists at M(2) and M(3) mAChRs. The biological profile of polyamines 4-7 revealed that increasing the number of amine functions and the chain length separating these nitrogen atoms led to a significant improvement in potency at nAChRs. Moreover, the role of the number and type of amine functions in the interaction with nAChRs was further investigated through the synthesis of compounds 9 and 10. Tetraamines 8 and 11, bearing a rather rigid spacer between the nitrogen atoms instead of the very flexible polymethylene chain, displayed a profile similar to that of 1 at nAChRs, whereas a significant decrease in potency was observed at mAChRs. Tetraamine 12, bearing a 2-methoxyphenethyl group, was less potent than 1, whereas tetraamine 13, carrying a diphenylethyl moiety, was more potent than 1, confirming that an increase in size of the hydrophobic group on the terminal nitrogen atoms increases significantly the binding affinity for nAChRs. Tetraamines 14-17 were significantly more potent than prototype 2 at both frog rectus and Torpedo nAChRs, confirming that an increase in the distance between the amine functions results in a parallel increase in the affinity for nAChRs. To gain insight into the mode of interaction of polymethylene tetraamines with nAChRs, photolabile (19 and 20) and fluorescent (21 and 22) compounds were synthesized. A most intriguing finding was the observation that 19, which bears two identical azido groups on the terminal nitrogen atoms, was found to bind the Torpedo nAChR with a 1:1 stoichiometry, suggesting a U-shaped conformation in the receptor interaction. Moreover, the high potency shown by fluorescent compounds 21 and 22 appears promising for a further characterization of the polymethylene tetraamines binding site with the muscle-type nAChR.

Prazosin-related compounds. Effect of transforming the piperazinylquinazoline moiety into an aminomethyltetrahydroacridine system on the affinity for alpha1-adrenoreceptors.

In a search for structurally new alpha(1)-adrenoreceptor (alpha(1)-AR) antagonists, prazosin (1)-related compounds 2-11 were synthesized and their affinity profiles were assessed by functional experiments in isolated rat vas deferens (alpha(1A)), spleen (alpha(1B)), and aorta (alpha(1D)) and by binding assays in CHO cells expressing human cloned alpha(1)-AR subtypes. Transformation of the piperazinylquinazoline moiety of 1 into an aminomethyltetrahydroacridine system afforded compound 2, endowed with reduced affinity, in particular for the alpha(1A)-AR subtype. Then, to investigate the optimal features of the tricyclic moiety, the aliphatic ring of 2 was modified by synthesizing the lower and higher homologues 3 and 4. An analysis of the pharmacological profile, together with a molecular modeling study, indicated the tetrahydroacridine moiety as the most promising skeleton for alpha(1)-antagonism. Compounds 5-8, where the replacement of the furoyl group of 2 with a benzoyl moiety afforded the possibility to evaluate the effect of the substituent trifluoromethyl on receptor binding, resulted, except for 7, in a rather surprising selectivity toward alpha(1B)-AR, in particular vs the alpha(1A) subtype. Also the insertion of the 2,6-dimethoxyphenoxyethyl function of WB 4101 on the tetrahydroacridine skeleton of 2, and/or the replacement of the aromatic amino function with a hydroxy group, affording derivatives 9-11, resulted in alpha(1B)-AR selectivity also vs the alpha(1D) subtype. On the basis of these results, the tetrahydroacridine moiety emerged as a promising tool for the characterization of the alpha(1)-AR, owing to the receptor subtype selectivity achieved by an appropriate modification of the lateral substituents.

Structure-activity relationships of methoctramine-related polyamines as muscular nicotinic receptor noncompetitive antagonists. 3. Effect of inserting the tetraamine backbone into a macrocyclic structure.

The present article expands on the study of another aspect of structure-activity relationships of the polymethylene tetraamines, namely, the effect of inserting the tetraamine backbone into a macrocyclic structure. To this end, compounds 8-12 were designed by linking the two terminal nitrogen atoms of prototype methoctramine 2 to an aryl moiety. Alternatively, 2 was first modified to achieve compounds 6 and 7, which in turn were cyclized by linking the two terminal primary amine functions to a polyphenyl spacer, affording 13-20. All the compounds were tested on muscle-type nAChRs and most of them as well on AChE. Furthermore, selected compounds were tested also on peripheral M(2) and M(3) mAChRs. All these cyclic derivatives, like prototypes, were potent noncompetitive antagonists at both frog and Torpedo nAChRs, suggesting that polyamines do not need to be linear or in extended conformation to optimally interact with the nicotinic channel; rather, they may bind in a U-shaped conformation. Relative to muscarinic activity, macrocyclic compounds 10, 13, 14, and 20, in contrast with the profile displayed by 2, were almost devoid of affinity. It is derived that an aryl spacer is detrimental to the interaction of polyamines with mAChRs. Finally, all the diamine diamides investigated in this study were much less potent in inhibiting AChE activity than prototype 3, suggesting that a macrocyclic structure may not be suitable for AChE inhibition.

Sequential virtual screening approach to the identification of small organic molecules as potential BACE-1 inhibitors.

In this letter, we report on the sequential application of two different in silico screening approaches combined with bioassays aimed at the identification of small organic molecules as potential BACE-1 inhibitors. Two hits endowed of micromolar inhibitory potency were selected, and the binding mode of the most potent compound was further characterized through docking simulations.

Alzheimer's disease: new approaches to drug discovery.

In this work, we review and comment upon the challenges and the 'quo vadis' in Alzheimer's disease drug discovery at the beginning of the new millennium. We emphasize recent approaches that, moving on from a target-centric approach, have produced innovative molecular probes or drug candidates. In particular, the discovery of endosome-targeted BACE1 inhibitors and mitochondria-targeted antioxidants represents a significant advance in Alzheimer's research and therapy. The case study of the development of rasagiline provides an excellent example to support the validity of the multitarget-designed ligand approach to the search for effective medicines for combating Alzheimer's disease.

Inhibition of acetylcholinesterase, beta-amyloid aggregation, and NMDA receptors in Alzheimer's disease: a promising direction for the multi-target-directed ligands gold rush.

Alzheimer's disease (AD) is a multifactorial syndrome with several target proteins contributing to its etiology. To confront AD, an innovative strategy is to design single chemical entities able to simultaneously modulate more than one target. Here, we present compounds that inhibit acetylcholinesterase and NMDA receptor activity. Furthermore, these compounds inhibit AChE-induced Abeta aggregation and display antioxidant properties, emerging as lead candidates for treating AD.

Recent advances in alpha1-adrenoreceptor antagonists as pharmacological tools and therapeutic agents.

Native alpha(1)-adrenoreceptors (ARs) appear to exist as three different subtypes encoded by three genes, alpha(1A/1a), alpha(1B/1b), and alpha(1D/1d). Historically, the discovery of agents selective for each of the three alpha(1)-AR subtypes has been an active area of medicinal chemistry research because of the wide number of possible therapeutic applications. Initially introduced for the management of hypertension, alpha(1)-AR antagonists have, in fact, become increasingly common in the treatment of benign prostatic hyperplasia (BPH), and are effective therapeutic tools, when characterized by an appropriate uroselective profile. The majority of these derivatives display a competitive mechanism of action and belong to a variety of structural classes, but this review is focused on compounds belonging to the quinazoline, benzodioxane, arylpiperazine, and 1,4-dihydropyridine classes.