Crystallographic and biochemical studies have been employed to identify the binding site and mechanism for potentiation of imidazoline binding in human monoamine oxidase B (MAO B). ...2-(2-Benzofuranyl)-2-imidazoline (2-BFI) inhibits recombinant human MAO B with a Ki of 8.3 ± 0.6 μm, whereas tranylcypromine-inhibited MAO B binds 2-BFI with a Kd of 9 ± 2 nm, representing an increase in binding energy Δ(ΔG) of −3.9 kcal/mol. Crystal structures show the imidazoline ligand bound in a site that is distinct from the substrate-binding cavity. Contributions to account for the increase in binding affinity upon tranylcypromine inhibition include a conformational change in the side chain of Gln206 and a “closed conformation” of the side chain of Ile199, forming a hydrophobic “sandwich” with the side chain of Ile316 on each face of the benzofuran ring of 2-BFI. Data with the I199A mutant of human MAO B and failure to observe a similar binding potentiation with rat MAO B, where Ile316 is replaced with a Val residue, support an allosteric mechanism where the increased binding affinity of 2-BFI results from a cooperative increase in H-bond strength through formation of a more hydrophobic milieu. These insights should prove valuable in the design of high affinity and specific reversible MAO B inhibitors.
Several reversible inhibitors selective for human monoamine oxidase B (MAO B) that do not inhibit MAO A have been described in the literature. The following compounds: 8-(3-chlorostyryl)caffeine, ...1,4-diphenyl-2-butene, and trans,trans-farnesol are shown to inhibit competitively human, horse, rat, and mouse MAO B with Ki values in the low micromolar range but are without effect on either bovine or sheep MAO B or human MAO A. In contrast, the reversible competitive inhibitor isatin binds to all known MAO B and MAO A with similar affinities. Sequence alignments and the crystal structures of human MAO B in complex with 1,4-diphenyl-2-butene or with trans,trans-farnesol provide molecular insights into these specificities. These inhibitors span the substrate and entrance cavities with the side chain of Ile-199 rotated out of its normal conformation suggesting that Ile-199 is gating the substrate cavity. Ile-199 is conserved in all known MAO B sequences except bovine MAO B, which has Phe in this position (the sequence of sheep MAO B is unknown). Phe is conserved in the analogous position in MAO A sequences. The human MAO B I199F mutant protein of MAO B binds to isatin (Ki = 3 μm) but not to the three inhibitors listed above. The crystal structure of this mutant demonstrates that the side chain of Phe-199 interferes with the binding of those compounds. This suggests that the Ile-199 “gate” is a determinant for the specificity of these MAO B inhibitors and provides a molecular basis for the development of MAO B-specific reversible inhibitors without interference with MAO A function in neurotransmitter metabolism.
: LSD1 is a lysine demethylase highly involved in initiation and development of cancer. To design highly effective covalent inhibitors, a strategy is to fill its large catalytic cleft by designing ...tranylcypromine (TCP) analogs decorated with long, hindered substituents. We prepared three series of TCP analogs, carrying aroyl‐ and arylacetylamino (1 a–h), Z‐amino acylamino (2 a–o), or double‐substituted benzamide (3 a–n) residues at the C4 or C3 position of the phenyl ring. Further fragments obtained by chemical manipulation applied on the TCP scaffold (compounds 4 a–i) were also prepared. When tested against LSD1, most of 1 and 3 exhibited IC50 values in the low nanomolar range, with 1 e and 3 a,d,f,g being also the most selective respect to monoamine oxidases. In MV4‐11 AML and NB4 APL cells compounds 3 were the most potent, displaying up to sub‐micromolar cell growth inhibition against both cell lines (3 a) or against NB4 cells (3 c). The most potent compounds in cellular assays were also able to induce the expression of LSD1 target genes, such as GFI‐1b, ITGAM, and KCTD12, as functional read‐out for LSD1 inhibition. Mouse and human intrinsic clearance data highlighted the high metabolic stability of compounds 3 a, 3 d and 3 g. Further studies will be performed on the new compounds 3 a and 3 c to assess their anticancer potential in different cancer contexts.
Some TCP for LSD: Lysine specific demethylase 1 (LSD1) is heavily involved in the initiation and progression of cancer. Through an X‐ray‐driven drug discovery process, we identified some tranylcypromine (TCP)‐based compounds 1–4. Among them, 1–3 were found to be active against LSD1 in the sub‐micromolar/low nanomolar range. When tested in MV4‐11 AML and NB4 APL cells, 3 a and 3 c were the most potent to arrest proliferation and induced target genes under the control of LSD1 in cells. These compounds will be further validated in different cancer contexts.
Current structural results of several flavin-dependent amine oxidizing enzymes including human monoamine oxidases A and B (MAO A and MAO B) show aromatic amino acid residues oriented approximately ...perpendicular to the flavin ring, suggesting a functional role in catalysis. In the case of human MAO B, two tyrosyl residues (Y398 and Y435) are found in the substrate binding site on the re face of the covalent flavin ring Binda et al. (2002) J. Biol. Chem. 277, 23973−23976. To probe the functional significance of this structure, Tyr435 in MAO B was mutated with the amino acids Phe, His, Leu, or Trp, the mutant proteins expressed in Pichia pastoris, and purified to homogeneity. Each mutant protein contains covalent FAD and exhibits a high level of catalytic functionality. No major alterations in active site structures are detected on comparison of their respective crystal structures with that of WT enzyme. The relative k cat/K m values for each mutant enzyme show Y435 > Y435F = Y435L = Y435H > Y435W. A similar behavior is also observed with the membrane-bound forms of MAO A and MAO B (MAO A Y444 mutant enzymes are found to be unstable on membrane extraction). p-Nitrobenzylamine is found to be a poor substrate while p-nitrophenethylamine is found to be a good substrate for all WT and mutant forms of MAO B. Analysis of these kinetic and structural data suggests the function of the “aromatic cage” in MAO to include a steric role in substrate binding and access to the flavin coenzyme and to increase the nucleophilicity of the substrate amine moiety. These results are consistent with a proposed polar nucleophilic mechanism for catalytic amine oxidation.
Human lysine-specific demethylase (LSD1) is a chromatin-modifying enzyme that specifically removes methyl groups from mono- and dimethylated Lys4 of histone H3 (H3-K4). We used a combination of in ...vivo and in vitro experiments to characterize the substrate specificity and recognition by LSD1. Biochemical assays on histone peptides show that essentially all epigenetic modifications on the 21 N-terminal amino acids of histone H3 cause a significant reduction in enzymatic activity. Replacement of Lys4 with Arg greatly enhances binding affinity, and a histone peptide incorporating this mutation has a strong inhibitory power. Conversely, a peptide bearing a trimethylated Lys4 is only a weak inhibitor of the enzyme. Rapid kinetics measurements evidence that the enzyme is efficiently reoxidized by molecular oxygen with a second-order rate constant of 9.6 × 103m-1 s-1, and that the presence of the reaction product does not greatly influence the rate of flavin reoxidation. In vivo experiments provide a correlation between the in vitro inhibitory properties of the tested peptides and their ability of affecting endogenous LSD1 activity. Our results show that epigenetic modifications on histone H3 need to be removed before Lys4 demethylation can efficiently occur. The complex formed by LSD1 with histone deacetylases 1/2 may function as a “double-blade razor” that first eliminates the acetyl groups from acetylated Lys residues and then removes the methyl group from Lys4. We suggest that after H3-K4 demethylation, LSD1 recruits the forthcoming chromatin remodelers leading to the introduction of gene repression marks.
Playing a pivotal role in the metabolism of neurotransmitters in the central nervous system, the mitochondrial enzymes monoamine oxidases A and B (MAO A and B) have been for long studied as drug ...targets for neurodegenerative and neurological diseases. MAO inhibitors (MAOIs) are clinically used to treat Parkinson's disease and depression by blocking the degradation of neuroactive catecholamines and providing a symptomatic relief in the patients. More recent is the idea that the neuroprotective effect of MAOIs may result from the prevention of oxidative stress produced by the MAO reaction rather than being simply related to the inhibition of neurotransmitters degradation. Tranylcypromine and phenelzine are among the first developed MAOI drugs and have been used for years to treat depression. Their usage is now limited to cases of refractory depression because of their negative side effects, which are due to both the lack of MAO A/MAO B selectivity and the inhibition of other enzymes such as the drug-metabolizing cytochromes P450. Although the multi-target action of these MAOIs determines negative implications, the most newly developed compounds have improved properties not only for their specificity relatively to MAO A/MAO B selectivity but also because they function through multiple mechanisms that produce beneficial effects. In particular, safinamide, a MAO B selective inhibitor in clinical trials for Parkinson's disease, is neuroprotective by blocking the voltage-dependent Na+ and Ca2+ channels and the Ca2+-mediated glutamate release processes. Rasagiline is a drug used in combination with L-dopa in the treatment of parkinsonian patients and the metabolic products of its degradation exert neuroprotective effects. Moreover, rasagiline scaffold is used to design analogs by addition of pharmacophores that act on other neurological targets. This multi-target approach may prove successful in order to find new and more effective therapies for the complexity of neurodegenerative diseases.
We describe the development of quinolylnitrones (QNs) as multifunctional ligands inhibiting cholinesterases (ChEs: acetylcholinesterase and butyrylcholinesterase–hBChE) and monoamine oxidases ...(hMAO-A/B) for the therapy of neurodegenerative diseases. We identified QN 19, a simple, low molecular weight nitrone, that is readily synthesized from commercially available 8-hydroxyquinoline-2-carbaldehyde. Quinolylnitrone 19 has no typical pharmacophoric element to suggest ChE or MAO inhibition, yet unexpectedly showed potent inhibition of hBChE (IC50 = 1.06 ± 0.31 nmol/L) and hMAO-B (IC50 = 4.46 ± 0.18 μmol/L). The crystal structures of 19 with hBChE and hMAO-B provided the structural basis for potent binding, which was further studied by enzyme kinetics. Compound 19 acted as a free radical scavenger and biometal chelator, crossed the blood–brain barrier, was not cytotoxic, and showed neuroprotective properties in a 6-hydroxydopamine cell model of Parkinson's disease. In addition, in vivo studies showed the anti-amnesic effect of 19 in the scopolamine-induced mouse model of AD without adverse effects on motoric function and coordination. Importantly, chronic treatment of double transgenic APPswe-PS1δE9 mice with 19 reduced amyloid plaque load in the hippocampus and cortex of female mice, underscoring the disease-modifying effect of QN 19.
Quinolylnitrone 19 was identified as a dual hBChE/hMAO-B inhibitor that improved cognition in scopolamine-induced mice model and reduced amyloid plaque load in cortex and hippocampus of APPswe/PS1δE9 mice. Display omitted
Monoamine oxidases A and B (MAO A and B) catalyze the degradation of neurotransmitters and represent drug targets for the treatment of neurodegenerative disorders. Rasagiline is an irreversible, MAO ...B-selective inhibitor that has been approved as a novel anti-Parkinson's drug. In this study, we investigate the inhibition of recombinant human MAO A and MAO B by several rasagiline analogues. Different substituents added onto the rasagiline scaffold alter the binding affinity depending on the position on the aminoindan ring and on the size of the substituent. Compounds with a hydroxyl group on either the C4 or the C6 atom inhibit both isozymes, whereas a bulkier substituent such as a carbamate is tolerated only at the C4 position. The 1.7 Å crystal structure of MAO B in complex with 4-(N-methyl-N-ethyl-carbamoyloxy)-N-methyl-N-propargyl-1(R)-aminoindan shows that the binding mode is similar to that of rasagiline with the carbamate moiety occupying the entrance cavity space. 1(R)-Aminoindan, the major metabolic product of rasagiline, and its analogues reversibly inhibit both MAO A and MAO B. The crystal structure of N-methyl-1(R)-aminoindan bound to MAO B shows that its aminoindan ring adopts a different orientation compared to that of rasagiline.
Background: Polyamines are essential for cell growth and differentiation; compounds interfering with their metabolism are potential anticancer agents. Polyamine oxidase (PAO) plays a central role in ...polyamine homeostasis. The enzyme utilises an FAD cofactor to catalyse the oxidation of the secondary amino groups of spermine and spermidine.
Results: The first crystal structure of a polyamine oxidase has been determined to a resolution of 1.9 Å. PAO from
Zea mays contains two domains, which define a remarkable 30 Ålong U-shaped catalytic tunnel at their interface. The structure of PAO in complex with the inhibitor MDL72527 reveals the residues forming the catalytic machinery and unusual enzyme-inhibitor CH···O H bonds. A ring of glutamate and aspartate residues surrounding one of the two tunnel openings contributes to the steering of the substrate towards the inside of the tunnel.
Conclusions: PAO specifically oxidises substrates that have both primary and secondary amino groups. The complex with MDL72527 shows that the primary amino groups are essential for the proper alignment of the substrate with respect to the flavin. Conservation of an N-terminal sequence motif indicates that PAO is member of a novel family of flavoenzymes. Among these, monoamine oxidase displays significant sequence homology with PAO, suggesting a similar overall folding topology.
A novel series of substituted chalcones were designed and synthesized to be evaluated as selective human MAO-B inhibitors. A combination of either methylsulfonyl or trifluoromethyl substituents on ...the aromatic ketone moiety with a benzodioxol ring on the other end of the chalcone scaffold was investigated. The compounds were tested for their inhibitory activities on both human MAO-A and B. All compounds appeared to be selective MAO-B inhibitors with Ki values in the micromolar to submicromolar range. Molecular modeling studies have been performed to get insight into the binding mode of the synthesized compounds to human MAO-B active site.
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•Novel chalcone analogs were designed and synthesized as human MAO-B reversible inhibitors.•The inhibitors bind with micromolar to submicromolar potency.•The molecular scaffold determines high MAO-A/MAO-B selectivity.•A double conformation in MAO-B active site is predicted by molecular docking.
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