Design, synthesis, and biological evaluation of novel oxadiazole- and thiazole-based histamine H3R ligands

Coumarin derivatives with potential anticancer and antibacterial activity: Design, synthesis, VEGFR-2 and DNA gyrase inhibition, and in silico studies

A series of coumarin derivatives were designed, synthesized, and evaluated for their antiproliferative activity. Compound 3e exhibited significant antiproliferative activity and was further evaluated at five doses at the National Cancer Institute. It effectively inhibited vascular endothelial growth factor receptor-2 (VEGFR-2) with an IC₅₀ value of 0.082 ± 0.004 µM compared with sorafenib. While compound 3e significantly downregulated total VEGFR-2 and its phosphorylation, it markedly reduced the HUVEC's migratory potential, resulting in a significant disruption in wound healing. Furthermore, compound 3e caused a 22.51-fold increment in total apoptotic level in leukemia cell line HL-60(TB) and a 6.91-fold increase in the caspase-3 level. Compound 3e also caused cell cycle arrest, mostly at the G1/S phase. Antibacterial activity was evaluated against Gram-positive and Gram-negative bacterial strains. Compound 3b was the most active derivative, with the same minimum inhibitory concentration and minimum bactericidal concentration value of 128 μg/mL against K. pneumonia and high stability in mammalian plasma. Moreover, compounds 3b and 3f inhibited Gram-negative DNA gyrase with IC₅₀  = 0.73 ± 0.05 and 1.13 ± 0.07 µM, respectively, compared to novobiocin with an IC₅₀ value of 0.17 ± 0.02 µM. The binding affinity and pattern of derivative 3e toward the VEGFR-2 active site and compounds 3a-c and 3f in the DNA gyrase active site were evaluated using molecular modeling. Overall, ADME studies of the synthesized coumarin derivatives displayed promising pharmacokinetic properties.

Synthesis of a novel triphenylamine-based multifunctional fluorescent probe for continuous recognition application

In this paper, a novel fluorescent probe, TPA-PAT, with continuous recognition based on triphenylamine was designed, synthesized, and characterized by NMR, IR, and fluorescence spectrophotometry techniques.

OLHA (Nα-oleoylhistamine) modulates activity of mouse brain histaminergic neurons

Histaminergic (HA) neurons are located in the tuberomamillary nucleus (TMN) of the posterior hypothalamus, from where they project throughout the whole brain to control wakefulness. We examined the effects of N^α-oleoylhistamine (OLHA), a non-enzymatic condensation product of oleic acid (OLA) and histamine, on activity of mouse HA neurons in brain slices. OLHA bidirectionally modulated the firing of HA neurons. At 10 nM OLHA inhibited or had no action, whereas at 1 μM it evoked excitatory and inhibitory responses. Inhibition was not seen in presence of the histamine receptor H3 (H₃R) antagonist clobenpropit and in calcium-free medium. Pre-incubation with a histamine-reuptake blocker prevented the decrease in firing by OLHA. OLHA-evoked increase in firing (EC₅₀ ∼44 nM) was insensitive to blockers of cannabinoid 1 and 2 receptors and of the capsaicin receptor, but was significantly impaired by the peroxisome proliferator-activated receptor-alpha (PPAR-alpha) antagonist MK886, which suppressed also the rise in intracellular calcium level caused by OLHA. The OLHA-evoked excitation was mimicked by synthetic PPAR-alpha agonists (gemfibrozil and GW7647) and was abolished by the PKA inhibitor H-89. The H₃R affinity (Ki) for histamine, measured in HEK293 cells with stable expression of human H₃R, was higher than for OLHA (Ki: 42 vs 310 nM, respectively). Expression of PPAR-alpha was not different between TMN regions of males and females, responses to OLHA did not differ. Molecular modelling of PPAR-alpha bound to either OLHA or OEA showed similar binding energies. These findings shed light on a novel biotransformation product of histamine which may play a role in health and disease.

Guided rational design with scaffold hopping leading to novel histamine H3 receptor ligands

During the past decades, histamine H₃ receptors have received widespread attention in pharmaceutical research due to their involvement in pathophysiology of several diseases such as neurodegenerative disorders. In this context, blocking of these receptors is of paramount importance in progression of such diseases. In the current investigation, novel histamine H₃ receptor ligands were designed by exploiting scaffold-hopping drug-design strategy. We inspected the designed molecules in terms of ADME properties, drug-likeness, as well as toxicity profiles. Additionally molecular docking and dynamics simulation studies were performed to predict binding mode and binding free energy calculations, respectively. Among the designed structures, we selected compound d2 and its demethylated derivative as examples for synthesis and affinity measurement. In vitro binding assays of the synthesized molecules demonstrated that d2 has lower binding affinity (K_i = 2.61 μM) in radioligand displacement assay to hH₃R than that of demethylated form (K_i = 12.53 μM). The newly designed compounds avoid of any toxicity predictors resulted from extended in silico and experimental studies, can offer another scaffold for histamine H₃R antagonists for further structure-activity relationship studies.

Biphenylalkoxyamine Derivatives-Histamine H3 Receptor Ligands with Butyrylcholinesterase Inhibitory Activity

Neurodegenerative diseases, e.g., Alzheimer’s disease (AD), are a key health problem in the aging population. The lack of effective therapy and diagnostics does not help to improve this situation. It is thought that ligands influencing multiple but interconnected targets can contribute to a desired pharmacological effect in these complex illnesses. Histamine H₃ receptors (H₃Rs) play an important role in the brain, influencing the release of important neurotransmitters, such as acetylcholine. Compounds blocking their activity can increase the level of these neurotransmitters. Cholinesterases (acetyl- and butyrylcholinesterase) are responsible for the hydrolysis of acetylcholine and inactivation of the neurotransmitter. Increased activity of these enzymes, especially butyrylcholinesterase (BuChE), is observed in neurodegenerative diseases. Currently, cholinesterase inhibitors: donepezil, rivastigmine and galantamine are used in the symptomatic treatment of AD. Thus, compounds simultaneously blocking H₃R and inhibiting cholinesterases could be a promising treatment for AD. Herein, we describe the BuChE inhibitory activity of H₃R ligands. Most of these compounds show high affinity for human H₃R (K_i < 150 nM) and submicromolar inhibition of BuChE (IC₅₀ < 1 µM). Among all the tested compounds, 19 (E153, 1-(5-([1,1′-biphenyl]-4-yloxy)pentyl)azepane) exhibited the most promising in vitro affinity for human H₃R, with a K_i value of 33.9 nM, and for equine serum BuChE, with an IC₅₀ of 590 nM. Moreover, 19 (E153) showed inhibitory activity towards human MAO B with an IC₅₀ of 243 nM. Furthermore, in vivo studies using the Passive Avoidance Task showed that compound 19 (E153) effectively alleviated memory deficits caused by scopolamine. Taken together, these findings suggest that compound 19 can be a lead structure for developing new anti-AD agents.

Discovery of Potential, Dual-Active Histamine H3 Receptor Ligands with Combined Antioxidant Properties

In an attempt to find new dual acting histamine H₃ receptor (H₃R) ligands, we designed a series of compounds, structurally based on previously described in our group, a highly active and selective human histamine H₃ receptor (hH₃R) ligand KSK63. As a result, 15 obtained compounds show moderate hH₃R affinity, the best being the compound 17 (hH₃R K_i = 518 nM). Docking to the histamine H₃R homology model revealed two possible binding modes, with key interactions retained in both cases. In an attempt to find possible dual acting ligands, selected compounds were tested for antioxidant properties. Compound 16 (hH₃R K_i = 592 nM) showed the strongest antioxidant properties at the concentration of 10⁻⁴ mol/L. It significantly reduced the amount of free radicals presenting 50–60% of ascorbic acid activity in the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, as well as showed antioxidative properties in the ferric reducing antioxidant power (FRAP) assay. Despite the yet unknown antioxidation mechanism and moderate hH₃R affinity, 16 (QD13) constitutes a starting point for the search of potential dual acting H₃R ligands-promising tools for the treatment of neurological disorders associated with increased neuronal oxidative stress.

Diaryl-substituted thiosemicarbazone: A potent scaffold for the development of New Delhi metallo-β-lactamase-1 inhibitors

The superbug infection caused by New Delhi metallo-β-lactamase (NDM-1) has become an emerging public health threat. Inhibition of NDM-1 has proven challenging due to its shuttling between pathogenic bacteria. A potent scaffold, diaryl-substituted thiosemicarbazone, was constructed and assayed with metallo-β-lactamases (MβLs). The obtained twenty-six molecules specifically inhibited NDM-1 with IC₅₀ 0.038-34.7 µM range (except 1e, 2e, and 3d), and 1c is the most potent inhibitor (IC₅₀ = 0.038 µM). The structure-activity relationship of synthetic thiosemicarbazones revealed that the diaryl-substitutes, specifically 2-pyridine and 2-hydroxylbenzene improved inhibitory activities of the inhibitors. The thiosemicarbazones exhibited synergistic antimycobacterial actions against E. coli-NDM-1, resulted a 2-512-fold reduction in MIC of meropenem, while 1c restored 16-256-, 16-, and 2-fold activity of the antibiotic on clinical isolates ECs, K. pneumonia and P. aeruginosa harboring NDM-1, respectively. Also, mice experiments showed that 1c had a synergistic antibacterial ability with meropenem, reduced the bacterial load clinical isolate EC08 in the spleen and liver. This work provided a highly promising scaffold for the development of NDM-1 inhibitors.

Synthesis and antiseizure effect evaluation of nonimidazole histamine H3 receptor antagonists containing the oxazole moiety

The use of histamine H₃ receptor (H₃ R) antagonists is becoming a promising therapeutic approach for epilepsy. In this paper, a series of novel nonimidazole H₃ R antagonists was synthesized and screened as antiepileptic drugs. All of these prepared antagonists displayed micromolar or submicromolar H₃ R antagonistic activities in the cAMP response element luciferase screening assay. Compounds 5a (IC₅₀  = 0.11 μM), 5b (IC₅₀  = 0.56 μM), and 5f (IC₅₀  = 0.78 μM) displayed the most potent H₃ R antagonistic activities, with considerable potency when compared with pitolisant (IC₅₀  = 0.51 μM). In the maximal electroshock (MES)-induced seizure model, compounds 5c, 5e, and 5g showed obvious protection for the electrostimulated mice, and the protection of 5g against the MES-induced seizures was fully abrogated when mice were cotreated with R-(α)-methyl-histamine, a central nervous system-penetrant H₃ R agonist, suggesting that the potential therapeutic effect of 5g was observed to work through H₃ R. These results indicate that the attempt to find a new antiepileptic drug among H₃ R antagonists is practicable, but it is necessary to consider the log P of the molecules to ensure penetration of the blood-brain barrier.

Novel pyrrolidinone derivative lacks claimed histamine H3 receptor stimulation in receptor binding and functional studies

Since the discovery and early characterization of the histamine H₃ receptor (H₃R) in the 1980's, predominantly imidazole-based agonists were presented to the scientific community such as N^α-methylhistamine (N^α-MeHA) or (R)-α-methylhistamine ((R)α-MeHA). Whereas therapeutic applications have been prompted for H₃R agonists such as treatment of pain, asthma and obesity, several drawbacks associated with imidazole-containing ligands makes the search for new agonists for this receptor demanding. Accordingly, high interest arose after publication of several pyrrolidindione-based, highly affine H₃R agonists within this journal that avoid the imidazole moiety and thus, presenting a novel type of potential pharmacophores (Ghoshal, Anirban et al., 2018). In our present study performed in two independent laboratories, we further evaluated the exposed lead-compound (EC₅₀ = 0.1 nM) of the previous research project with regards to pharmacological behavior at H₃R. Thereby, no binding affinity was observed in neither [³H]N^α-MeHA nor bodilisant displacement assays that contradicts the previously published activity. Additional functional exploration employing GTPγ[³⁵S], cAMP-accumulation assay and cAMP response element (CRE)-driven reporter gene assays exhibited slight partial agonist properties of such pyrrolidindiones but acting apart from the reported concentration range. We conclude, that the previously reported actions of such pyrrolidindiones result from an overestimation based on the method of measurement and thus, we cast doubt on the new pharmacophores with H₃R agonist activity.

Ligand-guided homology modeling drives identification of novel histamine H3 receptor ligands

In this study, we report a ligand-guided homology modeling approach allowing the analysis of relevant binding site residue conformations and the identification of two novel histamine H3 receptor ligands with binding affinity in the nanomolar range. The newly developed method is based on exploiting an essential charge interaction characteristic for aminergic G-protein coupled receptors for ranking 3D receptor models appropriate for the discovery of novel compounds through virtual screening.

Structural modifications and in vitro pharmacological evaluation of 4-pyridyl-piperazine derivatives as an active and selective histamine H3 receptor ligands

A novel series of 4-pyridylpiperazine derivatives with varying alkyl linker length and eastern part substituents proved to be potent histamine H₃ receptor (hH₃R) ligands in the nanomolar concentration range. While paying attention to their alkyl linker length, derivatives with a six methylene linker tend to be more potent than their five methylene homologues. Moreover, in the case of both phenoxyacetyl- and phenoxypropionyl- derivatives, an eight methylene linkers possess lower activity than their seven methylene homologues. However, in global analysis of collected data on the influence of alkyl linker length, a three methylene homologues appeared to be of highest hH₃R affinity among all described 4-pyridylpiperazine derivatives from our group up to date. In the case of biphenyl and benzophenone derivatives, compounds with para- substituted second aromatic ring were of higher affinity than their meta analogues. Interestingly, benzophenone derivative 18 showed the highest affinity among all tested compounds (hH₃R K_i = 3.12 nM). The likely protein-ligand interactions, responsible for their high affinity were demonstrated using molecular modeling techniques. Furthermore, selectivity, intrinsic activity at H₃R, as well as drug-like properties of selected ligands were evaluated using in vitro methods.

Histamine H3 receptor ligands by hybrid virtual screening, docking, molecular dynamics simulations, and investigation of their biological effects

Histamine H₃ receptors (H₃ R), belonging to G-protein coupled receptors (GPCR) class A superfamily, are responsible for modulating the release of histamine as well as of other neurotransmitters by a negative feedback mechanism mainly in the central nervous system (CNS). These receptors have gained increased attention as therapeutic target for several CNS related neurological diseases. In the current study, we aimed to identify novel H₃ R ligands using in silico virtual screening methods. To this end, a combination of ligand- and structure-based approaches was utilized for screening of ZINC database on the homology model of human H₃ R. Structural similarity- and pharmacophore-based approaches were employed to generate compound libraries. Various molecular modeling methodologies such as molecular docking and dynamics simulation along with different drug likeness filtering criteria were applied to select anti-H₃ R ligands as promising candidate molecules based on different known parent lead compounds. In vitro binding assays of the selected molecules demonstrated three of them being active within the micromolar and submicromolar K_i range. The current integrated computational and experimental methods used in this work can provide new general insights for systematic hit identification for novel anti-H₃ R agents from large compound libraries.