Carles Galdeano

Pyrano(3,2-c)quinoline-6-Chlorotacrine Hybrids as a Novel Family of Acetylcholinesterase- and β-Amyloid-Directed Anti-Alzheimer Compounds

Two isomeric series of dual binding site acetylcholinesterase (AChE) inhibitors have been designed, synthesized, and tested for their ability to inhibit AChE, butyrylcholinesterase, AChE-induced and self-induced beta-amyloid (Abeta) aggregation, and beta-secretase (BACE-1) and to cross blood-brain barrier. The new hybrids consist of a unit of 6-chlorotacrine and a multicomponent reaction-derived pyrano[3,2-c]quinoline scaffold as the active-site and peripheral-site interacting moieties, respectively, connected through an oligomethylene linker containing an amido group at variable position. Indeed, molecular modeling and kinetic studies have confirmed the dual site binding of these compounds. The new hybrids, and particularly 27, retain the potent and selective human AChE inhibitory activity of the parent 6-chlorotacrine while exhibiting a significant in vitro inhibitory activity toward the AChE-induced and self-induced Abeta aggregation and toward BACE-1, as well as ability to enter the central nervous system, which makes them promising anti-Alzheimer lead compounds.

Structure-Guided Design and Optimization of Small Molecules Targeting the Protein–Protein Interaction between the von Hippel–Lindau (VHL) E3 Ubiquitin Ligase and the Hypoxia Inducible Factor (HIF) Alpha Subunit with in Vitro Nanomolar Affinities

E3 ubiquitin ligases are attractive targets in the ubiquitin–proteasome system, however, the development of small-molecule ligands has been rewarded with limited success. The von Hippel–Lindau protein (pVHL) is the substrate recognition subunit of the VHL E3 ligase that targets HIF-1α for degradation. We recently reported inhibitors of the pVHL:HIF-1α interaction, however they exhibited moderate potency. Herein, we report the design and optimization, guided by X-ray crystal structures, of a ligand series with nanomolar binding affinities.

Huprine–Tacrine Heterodimers as Anti-Amyloidogenic Compounds of Potential Interest against Alzheimer’s and Prion Diseases

A family of huprine-tacrine heterodimers has been developed to simultaneously block the active and peripheral sites of acetylcholinesterase (AChE). Their dual site binding for AChE, supported by kinetic and molecular modeling studies, results in a highly potent inhibition of the catalytic activity of human AChE and, more importantly, in the in vitro neutralization of the pathological chaperoning effect of AChE toward the aggregation of both the β-amyloid peptide (Aβ) and a prion peptide with a key role in the aggregation of the prion protein. Huprine-tacrine heterodimers take on added value in that they display a potent in vitro inhibitory activity toward human butyrylcholinesterase, self-induced Aβ aggregation, and β-secretase. Finally, they are able to cross the blood-brain barrier, as predicted in an artificial membrane model assay and demonstrated in ex vivo experiments with OF1 mice, reaching their multiple biological targets in the central nervous system. Overall, these compounds are promising lead compounds for the treatment of Alzheimers and prion diseases.

Tacrine-based dual binding site acetylcholinesterase inhibitors as potential disease-modifying anti-Alzheimer drug candidates.

Two novel families of dual binding site acetylcholinesterase (AChE) inhibitors have been developed, consisting of a tacrine or 6-chlorotacrine unit as the active site interacting moiety, either the 5,6-dimethoxy-2-[(4-piperidinyl)methyl]-1-indanone fragment of donepezil (or the indane derivative thereof) or a 5-phenylpyrano[3,2-c]quinoline system, reminiscent to the tryciclic core of propidium, as the peripheral site interacting unit, and a linker of suitable length as to allow the simultaneous binding at both sites. These hybrid compounds are all potent and selective inhibitors of human AChE, and more interestingly, are able to interfere in vitro both formation and aggregation of the beta-amyloid peptide, the latter effects endowing these compounds with the potential to modify Alzheimers disease progression.

Novel huprine derivatives with inhibitory activity toward β-amyloid aggregation and formation as disease-modifying anti-Alzheimer drug candidates.

A new family of dual binding site acetylcholinesterase (AChE) inhibitors has been designed, synthesized, and tested for their ability to inhibit AChE, butyrylcholinesterase (BChE), AChE‐induced and self‐induced β‐amyloid (Aβ) aggregation and β‐secretase (BACE‐1), and to cross the blood–brain barrier. The new heterodimers consist of a unit of racemic or enantiopure huprine Y or X and a donepezil‐related 5,6‐dimethoxy‐2‐[(4‐piperidinyl)methyl]indane moiety as the active site and peripheral site to mid‐gorge‐interacting moieties, respectively, connected through a short oligomethylene linker. Molecular dynamics simulations and kinetics studies support the dual site binding to AChE. The new heterodimers are potent inhibitors of human AChE and moderately potent inhibitors of human BChE, AChE‐induced and self‐induced Aβ aggregation, and BACE‐1, and are predicted to be able to enter the central nervous system (CNS), thus constituting promising multitarget anti‐Alzheimer drug candidates with the potential to modify the natural course of this disease.

Structural Determinants of the Multifunctional Profile of Dual Binding Site Acetylcholinesterase Inhibitors as Anti-Alzheimer Agents

Dual binding site acetylcholinesterase inhibitors have recently emerged as a new class of anti-Alzheimer agents with potential to positively modify the course of the disease. These compounds exhibit a multifunctional pharmacological profile arising from interaction with several biological targets involved upstream and downstream in the neurodegenerative cascade of Alzheimers disease (AD). The primary target of these compounds is the enzyme acetylcholinesterase (AChE). Interaction of dual binding site AChE inhibitors with AChE results in a potent inhibitory activity of AChE and AChE-induced β-amyloid peptide (Aβ) aggregation. Some dual binding site AChE inhibitors take on added value a significant ability to additionally inhibit the enzymes butyrylcholinesterase and BACE-1, involved in the co-regulation of the hydrolysis of the neurotransmitter acetylcholine and in Aβ formation, respectively. The structural determinants which mediate the interaction of dual binding site AChE inhibitors with these three important enzymes for AD treatment are herein reviewed.

Is NMR Fragment Screening Fine-Tuned to Assess Druggability of Protein-Protein Interactions?

Modulation of protein–protein interactions (PPIs) with small molecules has been hampered by a lack of lucid methods capable of reliably identifying high-quality hits. In fragment screening, the low ligand efficiencies associated with PPI target sites pose significant challenges to fragment binding detection. Here, we investigate the requirements for ligand-based NMR techniques to detect rule-of-three compliant fragments that form part of known high-affinity inhibitors of the PPI between the von Hippel–Lindau protein and the alpha subunit of hypoxia-inducible factor 1 (pVHL:HIF-1α). Careful triaging allowed rescuing weak but specific binding of fragments that would otherwise escape detection at this PPI. Further structural information provided by saturation transfer difference (STD) group epitope mapping, protein-based NMR, competitive isothermal titration calorimetry (ITC), and X-ray crystallography confirmed the binding mode of the rescued fragments. Our findings have important implications for PPI druggability assessment by fragment screening as they reveal an accessible threshold for fragment detection and validation.

Potent and selective chemical probe of hypoxic signalling downstream of HIF-α hydroxylation via VHL inhibition

Chemical strategies to using small molecules to stimulate hypoxia inducible factors (HIFs) activity and trigger a hypoxic response under normoxic conditions, such as iron chelators and inhibitors of prolyl hydroxylase domain (PHD) enzymes, have broad-spectrum activities and off-target effects. Here we disclose VH298, a potent VHL inhibitor that stabilizes HIF-α and elicits a hypoxic response via a different mechanism, that is the blockade of the VHL:HIF-α protein–protein interaction downstream of HIF-α hydroxylation by PHD enzymes. We show that VH298 engages with high affinity and specificity with VHL as its only major cellular target, leading to selective on-target accumulation of hydroxylated HIF-α in a concentration- and time-dependent fashion in different cell lines, with subsequent upregulation of HIF-target genes at both mRNA and protein levels. VH298 represents a high-quality chemical probe of the HIF signalling cascade and an attractive starting point to the development of potential new therapeutics targeting hypoxia signalling.

Selectivity on-target of bromodomain chemical probes by structure-guided medicinal chemistry and chemical biology

Targeting epigenetic proteins is a rapidly growing area for medicinal chemistry and drug discovery. Recent years have seen an explosion of interest in developing small molecules binding to bromodomains, the readers of acetyl-lysine modifications. A plethora of co-crystal structures has motivated focused fragment-based design and optimization programs within both industry and academia. These efforts have yielded several compounds entering the clinic, and many more are increasingly being used as chemical probes to interrogate bromodomain biology. High selectivity of chemical probes is necessary to ensure biological activity is due to an on-target effect. Here, we review the state-of-the-art of bromodomain-targeting compounds, focusing on the structural basis for their on-target selectivity or lack thereof. We also highlight chemical biology approaches to enhance on-target selectivity.

Thioflavin-S Staining of Bacterial Inclusion Bodies for the Fast, Simple, and Inexpensive Screening of Amyloid Aggregation Inhibitors

Amyloid aggregation is linked to a large number of human disorders, from neurodegenerative diseases as Alzheimers disease (AD) or spongiform encephalopathies to non-neuropathic localized diseases as type II diabetes and cataracts. Because the formation of insoluble inclusion bodies (IBs) during recombinant protein production in bacteria has been recently shown to share mechanistic features with amyloid self-assembly, bacteria have emerged as a tool to study amyloid aggregation. Herein we present a fast, simple, inexpensive and quantitative method for the screening of potential anti-aggregating drugs. This method is based on monitoring the changes in the binding of thioflavin-S to intracellular IBs in intact Eschericchia coli cells in the presence of small chemical compounds. This in vivo technique fairly recapitulates previous in vitro data. Here we mainly use the Alzheimers related β-amyloid peptide as a model system, but the technique can be easily implemented for screening inhibitors relevant for other conformational diseases simply by changing the recombinant amyloid protein target. Indeed, we show that this methodology can be also applied to the evaluation of inhibitors of the aggregation of tau protein, another amyloidogenic protein with a key role in AD.