Discovery of Novel Inhibitors of Uridine Diphosphate-N-Acetylenolpyruvylglucosamine Reductase (MurB) from Pseudomonas aeruginosa, an Opportunistic Infectious Agent Causing Death in Cystic Fibrosis Patients.

Pseudomonas aeruginosa is of major concern for cystic fibrosis patients where this infection can be fatal. With the emergence of drug-resistant strains, there is an urgent need to develop novel antibiotics against P. aeruginosa. MurB is a promising target for novel antibiotic development as it is involved in the cell wall biosynthesis. MurB has been shown to be essential in P. aeruginosa, and importantly, no MurB homologue exists in eukaryotic cells. A fragment-based drug discovery approach was used to target Pa MurB. This led to the identification of a number of fragments, which were shown to bind to MurB. One fragment, a phenylpyrazole scaffold, was shown by ITC to bind with an affinity of Kd = 2.88 mM (LE 0.23). Using a structure guided approach, different substitutions were synthesized and the initial fragment was optimized to obtain a small molecule with Kd = 3.57 µM (LE 0.35).

Tetrasubstituted Imidazolium Salts as Potent Antiparasitic Agents against African and American Trypanosomiases.

Imidazolium salts are privileged compounds in organic chemistry, and have valuable biological properties. Recent studies show that symmetric imidazolium salts with bulky moieties can display antiparasitic activity against T. cruzi. After developing a facile methodology for the synthesis of tetrasubstituted imidazolium salts from propargylamines and isocyanides, we screened a small library of these adducts against the causative agents of African and American trypanosomiases. These compounds display nanomolar activity against T. brucei and low (or sub) micromolar activity against T. cruzi, with excellent selectivity indexes and favorable molecular properties, thereby emerging as promising hits for the treatment of Chagas disease and sleeping sickness.

Correction: Unveiling a novel transient druggable pocket in BACE-1 through molecular simulations: Conformational analysis and binding mode of multisite inhibitors.

[This corrects the article DOI: 10.1371/journal.pone.0177683.].

Unveiling a novel transient druggable pocket in BACE-1 through molecular simulations: Conformational analysis and binding mode of multisite inhibitors.

The critical role of BACE-1 in the formation of neurotoxic ß-amyloid peptides in the brain makes it an attractive target for an efficacious treatment of Alzheimer's disease. However, the development of clinically useful BACE-1 inhibitors has proven to be extremely challenging. In this study we examine the binding mode of a novel potent inhibitor (compound 1, with IC50 80 nM) designed by synergistic combination of two fragments-huprine and rhein-that individually are endowed with very low activity against BACE-1. Examination of crystal structures reveals no appropriate binding site large enough to accommodate 1. Therefore we have examined the conformational flexibility of BACE-1 through extended molecular dynamics simulations, paying attention to the highly flexible region shaped by loops 8-14, 154-169 and 307-318. The analysis of the protein dynamics, together with studies of pocket druggability, has allowed us to detect the transient formation of a secondary binding site, which contains Arg307 as a key residue for the interaction with small molecules, at the edge of the catalytic cleft. The formation of this druggable "floppy" pocket would enable the binding of multisite inhibitors targeting both catalytic and secondary sites. Molecular dynamics simulations of BACE-1 bound to huprine-rhein hybrid compounds support the feasibility of this hypothesis. The results provide a basis to explain the high inhibitory potency of the two enantiomeric forms of 1, together with the large dependence on the length of the oligomethylenic linker. Furthermore, the multisite hypothesis has allowed us to rationalize the inhibitory potency of a series of tacrine-chromene hybrid compounds, specifically regarding the apparent lack of sensitivity of the inhibition constant to the chemical modifications introduced in the chromene unit. Overall, these findings pave the way for the exploration of novel functionalities in the design of optimized BACE-1 multisite inhibitors.

Design, synthesis and biological evaluation of N-methyl-N-[(1,2,3-triazol-4-yl)alkyl]propargylamines as novel monoamine oxidase B inhibitors.

Different azides and alkynes have been coupled via Cu-catalyzed 1,3-dipolar Huisgen cycloaddition to afford a novel family of N1- and C5-substituted 1,2,3-triazole derivatives that feature the propargylamine group typical of irreversible MAO-B inhibitors at the C4-side chain of the triazole ring. All the synthesized compounds were evaluated against human MAO-A and MAO-B. Structure-activity relationships and molecular modeling were utilized to gain insight into the structural and chemical features that enhance the binding affinity and selectivity between the two enzyme isoforms. Several lead compounds, in terms of potency (submicromolar to low micromolar range), MAO-B selective recognition, and brain permeability, were identified. One of these leads (MAO-B IC50 of 3.54µM, selectivity MAO-A/MAO-B index of 27.7) was further subjected to reversibility and time-dependence inhibition studies, which disclosed a slow and irreversible inhibition of human MAO-B. Overall, the results support the suitability of the 4-triazolylalkyl propargylamine scaffold for exploring the design of multipotent anti-Alzheimer compounds endowed with irreversible MAO-B inhibitory activity.

Ultra rapid in vivo screening for anti-Alzheimer anti-amyloid drugs.

More than 46 million people worldwide suffer from Alzheimer's disease. A large number of potential treatments have been proposed; among these, the inhibition of the aggregation of amyloid ß-peptide (Aß), considered one of the main culprits in Alzheimer's disease. Limitations in monitoring the aggregation of Aß in cells and tissues restrict the screening of anti-amyloid drugs to in vitro studies in most cases. We have developed a simple but powerful method to track Aß aggregation in vivo in real-time, using bacteria as in vivo amyloid reservoir. We use the specific amyloid dye Thioflavin-S (Th-S) to stain bacterial inclusion bodies (IBs), in this case mainly formed of Aß in amyloid conformation. Th-S binding to amyloids leads to an increment of fluorescence that can be monitored. The quantification of the Th-S fluorescence along the time allows tracking Aß aggregation and the effect of potential anti-aggregating agents.

Multicomponent reaction-based synthesis and biological evaluation of tricyclic heterofused quinolines with multi-trypanosomatid activity.

Human African trypanosomiasis (HAT), Chagas disease and leishmaniasis, which are caused by the trypanosomatids Trypanosoma brucei, Trypanosoma cruzi and Leishmania species, are among the most deadly neglected tropical diseases. The development of drugs that are active against several trypanosomatids is appealing from a clinical and economic viewpoint, and seems feasible, as these parasites share metabolic pathways and hence might be treatable by common drugs. From benzonapthyridine 1, an inhibitor of acetylcholinesterase (AChE) for which we have found a remarkable trypanocidal activity, we have designed and synthesized novel benzo[h][1,6]naphthyridines, pyrrolo[3,2-c]quinolines, azepino[3,2-c]quinolines, and pyrano[3,2-c]quinolines through 2-4-step sequences featuring an initial multicomponent Povarov reaction as the key step. To assess the therapeutic potential of the novel compounds, we have evaluated their in vitro activity against T. brucei, T. cruzi, and Leishmania infantum, as well as their brain permeability, which is of specific interest for the treatment of late-stage HAT. To assess their potential toxicity, we have determined their cytotoxicity against rat myoblast L6 cells and their AChE inhibitory activity. Several tricyclic heterofused quinoline derivatives were found to display an interesting multi-trypanosomatid profile, with one-digit micromolar potencies against two of these parasites and two-digit micromolar potency against the other. Pyranoquinoline 39, which displays IC50 values of 1.5 µM, 6.1 µM and 29.2 µM against T. brucei, L. infantum and T. cruzi, respectively, brain permeability, better drug-like properties (lower lipophilicity and molecular weight and higher CNS MPO desirability score) than hit 1, and the lowest AChE inhibitory activity of the series (IC50 > 30 µM), emerges as an interesting multi-trypanosomatid lead, amenable to further optimization particularly in terms of its selectivity index over mammalian cells.

Novel Levetiracetam Derivatives That Are Effective against the Alzheimer-like Phenotype in Mice: Synthesis, in Vitro, ex Vivo, and in Vivo Efficacy Studies.

We have synthesized a series of heptamethylene-linked levetiracetam-huprine and levetiracetam-(6-chloro)tacrine hybrids to hit amyloid, tau, and cholinergic pathologies as well as ß-amyloid (Aß)-induced epileptiform activity, some of the mechanisms that eventually lead to cognitive deficits in Alzheimer's disease patients. These hybrids are potent inhibitors of human acetylcholinesterase and butyrylcholinesterase in vitro and moderately potent Aß42 and tau antiaggregating agents in a simple E. coli model of amyloid aggregation. Ex vivo determination of the brain acetylcholinesterase inhibitory activity of these compounds after intraperitoneal injection to C57BL6J mice has demonstrated their ability to enter the brain. The levetiracetam-huprine hybrid 10 significantly reduced the incidence of epileptic seizures, cortical amyloid burden, and neuroinflammation in APP/PS1 mice after a 4-week treatment with a 5 mg/kg dose. Moreover, the hybrid 10 rescued transgenic mice from cognitive deficits, thereby emerging as an interesting disease-modifying anti-Alzheimer drug candidate.

Shogaol-huprine hybrids: dual antioxidant and anticholinesterase agents with ß-amyloid and tau anti-aggregating properties.

Multitarget compounds are increasingly being pursued for the effective treatment of complex diseases. Herein, we describe the design and synthesis of a novel class of shogaol-huprine hybrids, purported to hit several key targets involved in Alzheimer's disease. The hybrids have been tested in vitro for their inhibitory activity against human acetylcholinesterase and butyrylcholinesterase and antioxidant activity (ABTS.+, DPPH and Folin-Ciocalteu assays), and in intact Escherichia coli cells for their Aß42 and tau anti-aggregating activity. Also, their brain penetration has been assessed (PAMPA-BBB assay). Even though the hybrids are not as potent AChE inhibitors or antioxidant agents as the parent huprine Y and [4]-shogaol, respectively, they still exhibit very potent anticholinesterase and antioxidant activities and are much more potent Aß42 and tau anti-aggregating agents than the parent compounds. Overall, the shogaol-huprine hybrids emerge as interesting brain permeable multitarget anti-Alzheimer leads.

Tetrahydrobenzo[h][1,6]naphthyridine-6-chlorotacrine hybrids as a new family of anti-Alzheimer agents targeting ß-amyloid, tau, and cholinesterase pathologies.

Optimization of an essentially inactive 3,4-dihydro-2H-pyrano[3,2-c]quinoline carboxylic ester derivative as acetylcholinesterase (AChE) peripheral anionic site (PAS)-binding motif by double O → NH bioisosteric replacement, combined with molecular hybridization with the AChE catalytic anionic site (CAS) inhibitor 6-chlorotacrine and molecular dynamics-driven optimization of the length of the linker has resulted in the development of the trimethylene-linked 1,2,3,4-tetrahydrobenzo[h][1,6]naphthyridine-6-chlorotacrine hybrid 5a as a picomolar inhibitor of human AChE (hAChE). The tetra-, penta-, and octamethylene-linked homologues 5b-d have been also synthesized for comparison purposes, and found to retain the nanomolar hAChE inhibitory potency of the parent 6-chlorotacrine. Further biological profiling of hybrids 5a-d has shown that they are also potent inhibitors of human butyrylcholinesterase and moderately potent Aß42 and tau anti-aggregating agents, with IC50 values in the submicromolar and low micromolar range, respectively. Also, in vitro studies using an artificial membrane model have predicted a good brain permeability for hybrids 5a-d, and hence, their ability to reach their targets in the central nervous system. The multitarget profile of the novel hybrids makes them promising leads for developing anti-Alzheimer drug candidates with more balanced biological activities.

1,2,3,4-Tetrahydrobenzo[h][1,6]naphthyridines as a new family of potent peripheral-to-midgorge-site inhibitors of acetylcholinesterase: synthesis, pharmacological evaluation and mechanistic studies.

A series of 1,2,3,4-tetrahydrobenzo[h][1,6]naphthyridines differently substituted at positions 1, 5, and 9 have been designed from the pyrano[3,2-c]quinoline derivative 1, a weak inhibitor of acetylcholinesterase (AChE) with predicted ability to bind to the AChE peripheral anionic site (PAS), at the entrance of the catalytic gorge. Fourteen novel benzonaphthyridines have been synthesized through synthetic sequences involving as the key step a multicomponent Povarov reaction between an aldehyde, an aniline and an enamine or an enamide as the activated alkene. The novel compounds have been tested against Electrophorus electricus AChE (EeAChE), human recombinant AChE (hAChE), and human serum butyrylcholinesterase (hBChE), and their brain penetration has been assessed using the PAMPA-BBB assay. Also, the mechanism of AChE inhibition of the most potent compounds has been thoroughly studied by kinetic studies, a propidium displacement assay, and molecular modelling. We have found that a seemingly small structural change such as a double O â†’ NH bioisosteric replacement from the hit 1 to 16a results in a dramatic increase of EeAChE and hAChE inhibitory activities (>217- and >154-fold, respectively), and in a notable increase in hBChE inhibitory activity (>11-fold), as well. An optimized binding at the PAS besides additional interactions with AChE midgorge residues seem to account for the high hAChE inhibitory potency of 16a (IC50 = 65 nM), which emerges as an interesting anti-Alzheimer lead compound with potent dual AChE and BChE inhibitory activities.