Optimization and preclinical evaluation of novel histamine H3receptor ligands: Acetyl and propionyl phenoxyalkyl piperazine derivatives

Design, Synthesis and Biological Evaluation of Novel N-Arylpiperazines Containing a 4,5-Dihydrothiazole Ring

Arylpiperazines represent one of the most important classes of 5-HT1AR ligands and have attracted considerable interests for their versatile properties in chemistry and pharmacology, leading to the research of new derivatives that has been focused on the modification of one or more portions of such pharmacophore. An efficient protocol for the synthesis of novel thiazolinylphenyl-piperazines (2a-c) and the corresponding acetylated derivatives was used (3a-c). The new compounds were tested for their functional activity and affinity at 5-HT1A receptors, showing an interesting affinity profile with a Ki value of 412 nM for compound 2b. The cytotoxic activity of novel thiazolinylphenyl-piperazines (2a-c) and corresponding N-acetyl derivatives (3a-c) against human prostate and breast cancer cell lines (LNCAP, DU-145 and PC-3, MCF-7, SKBR-3 and MDA-MB231) was investigated according to the procedure described in the literature. The reported data showed a cytotoxic effect for 2a-c and 3a-c compounds (IC50 values ranging from 15 µM to 73 µM) on the investigated cancer cell lines, with no effect on noncancer cells. Future studies will be aimed to investigate the mechanism of action and therapeutic prospects of these new scaffolds.

KSK-74: Dual Histamine H3 and Sigma-2 Receptor Ligand with Anti-Obesity Potential

Many studies involving compounds that enhance histamine release, such as histamine H₃ receptor (H₃R) antagonists, have shown efficacy in inhibiting weight gain, but none have passed clinical trials. As part of the search for H₃ receptor ligands that have additional properties, the aim of this study is to evaluate the activity in the reduction in weight gain in a rat model of excessive eating, as well as the impact on selected metabolic parameters, and the number and size of adipocytes of two new H₃R antagonists, KSK-60 and KSK-74, which also exert a significant affinity at the sigma-2 receptor. Compounds KSK-60 and KSK-74 are homologues and the elongation of the distal part of the molecule resulted in an approximate two-fold reduction in affinity at H₃R, but simultaneously an almost two-fold increase in affinity at the sigma-2 receptor. Animals fed palatable feed and receiving KSK-60 or KSK-74 both at 10 mg/kg b.w. gained significantly less weight than animals in the control obese group. Moreover, KSK-74 significantly compensated for metabolic disturbances that accompany obesity, such as an increase in plasma triglyceride, resistin, and leptin levels; improved glucose tolerance; and protected experimental animals against adipocyte hypertrophy. Furthermore, KSK-74 inhibited the development of inflammation in obesity-exposed adipose tissue. The in vivo pharmacological activity of the tested ligands appears to correlate with the affinity at the sigma-2 receptors; however, the explanation of this phenomenon requires further and extended research.

Structural and Molecular Insight into Piperazine and Piperidine Derivatives as Histamine H3 and Sigma-1 Receptor Antagonists with Promising Antinociceptive Properties

In an attempt to extend recent studies showing that some clinically evaluated histamine H3 receptor (H3R) antagonists possess nanomolar affinity at sigma-1 receptors (σ1R), we selected 20 representative structures among our previously reported H3R ligands to investigate their affinity at σRs. Most of the tested compounds interact with both sigma receptors to different degrees. However, only six of them showed higher affinity toward σ1R than σ2R with the highest binding preference to σ1R for compounds 5, 11, and 12. Moreover, all these ligands share a common structural feature: the piperidine moiety as the fundamental part of the molecule. It is most likely a critical structural element for dual H3/σ1 receptor activity as can be seen by comparing the data for compounds 4 and 5 (hH3R Ki = 3.17 and 7.70 nM, σ1R Ki = 1531 and 3.64 nM, respectively), where piperidine is replaced by piperazine. We identified the putative protein-ligand interactions responsible for their high affinity using molecular modeling techniques and selected compounds 5 and 11 as lead structures for further evaluation. Interestingly, both ligands turned out to be high-affinity histamine H3 and σ1 receptor antagonists with negligible affinity at the other histamine receptor subtypes and promising antinociceptive activity in vivo. Considering that many literature data clearly indicate high preclinical efficacy of individual selective σ1 or H3R ligands in various pain models, our research might be a breakthrough in the search for novel, dual-acting compounds that can improve existing pain therapies. Determining whether such ligands are more effective than single-selective drugs will be the subject of our future studies.

Metabolic benefits of novel histamine H3 receptor ligands in the model of excessive eating: The importance of intrinsic activity and pharmacokinetic properties

AIMS

One of the therapeutic approaches in the treatment of obesity is the use of histamine H3 receptor ligands. Histamine plays a significant role in eating behavior because it causes a loss of appetite and is considered to be a satiety signal released during food intake.

MATERIAL AND METHODS

Histamine ligands were selected based on the preliminary studies which included determination of intrinsic activity and selected pharmacokinetic parameters. Female Wistar rats were fed palatable feed for 28 days and simultaneously the tested compounds were administered intraperitoneally at a dose of 10 mg/kg b.w./day. Rats' weight was evaluated daily and calories intake was evaluated once per week. At the end of experiment insulin and glucose tolerance tests was performed. Plasma levels of cholesterol, triglycerides, leptin, insulin, glucose, C-peptide and CRP were also determined. In order to rule out false-positive results the influence of tested compounds on spontaneous activity of rats was monitored.

RESULTS

Animals fed palatable feed and treated with KSK-61 or KSK-63 compounds showed the slowest weight gain which was comparable to the one observed in control animals. Both compounds with the highest pharmacological activity have also similar pharmacokinetic properties with quite long half-life and high volume of distribution indicating that they can freely cross most biological barriers. Some compounds, especially KSK-63, compensated for metabolic disorders.

CONCLUSION

The presented study proves that search among the active histamine H3 receptor ligands for the new therapeutic agents to treat obesity is justified. Compounds KSK-61 and KSK-63 can be considered as the leading structures.

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.

Molecular Modeling of Histamine Receptors-Recent Advances in Drug Discovery

The recent developments of fast reliable docking, virtual screening and other algorithms gave rise to discovery of many novel ligands of histamine receptors that could be used for treatment of allergic inflammatory disorders, central nervous system pathologies, pain, cancer and obesity. Furthermore, the pharmacological profiles of ligands clearly indicate that these receptors may be considered as targets not only for selective but also for multi-target drugs that could be used for treatment of complex disorders such as Alzheimer's disease. Therefore, analysis of protein-ligand recognition in the binding site of histamine receptors and also other molecular targets has become a valuable tool in drug design toolkit. This review covers the period 2014-2020 in the field of theoretical investigations of histamine receptors mostly based on molecular modeling as well as the experimental characterization of novel ligands of these receptors.

Structural modifications in the distal, regulatory region of histamine H3 receptor antagonists leading to the identification of a potent anti-obesity agent

A series of 4-pyridylpiperazine derivatives with varying regulatory region substituents proved to be potent histamine H3 receptor (H3R) ligands in the nanomolar concentration range. The most influential modification that affected the affinity toward the H3R appeared by introducing electron-withdrawing moieties into the distal aromatic ring. In order to finally discuss the influence of the characteristic 4-pyridylpiperazine moiety on H3R affinity, two Ciproxifan analogues 2 and 3 with a slight modification in their basic part were obtained. The replacement of piperazine in 3 with piperidine in compound 2, led to slightly reduced affinity towards the H3R (Ki = 3.17 and 7.70 nM, respectively). In fact, 3 showed the highest antagonistic properties among all compounds in this series, hence affirming our previous assumptions, that the 4-pyridylpiperazine moiety is the key element for suitable interaction with the human histamine H3 receptor. While its structural replacement to piperidine is also tolerated for H3R binding, the heteroaromatic 4-pyridyl moiety seems to be essential for proper ligand-receptor interaction. The putative protein-ligand interactions responsible for their high affinity were demonstrated using molecular modeling techniques. Furthermore, selectivity, intrinsic activity at the H3R, as well as drug-like properties of ligands were evaluated using in vitro methods. Moreover, pharmacological in vivo test results of compound 9 (structural analogue of Abbott's A-331440) clearly indicate that it may affect the amount of calories consumed, thus act as an anorectic compound.

2-Pentadecyl-2-oxazoline ameliorates memory impairment and depression-like behaviour in neuropathic mice: possible role of adrenergic alpha2- and H3 histamine autoreceptors

Neuropathic pain (NP) remains an untreatable disease due to the complex pathophysiology that involves the whole pain neuraxis including the forebrain. Sensory dysfunctions such as allodynia and hyperalgesia are only part of the symptoms associated with neuropathic pain that extend to memory and affectivity deficits. The development of multi-target molecules might be a promising therapeutic strategy against the symptoms associated with NP. 2-pentadecyl-2-oxazoline (PEA-OXA) is a plant-derived agent, which has shown effectiveness against chronic pain and associated neuropsychiatric disorders. The molecular mechanisms by which PEA-OXA exerts its effects are, however, only partially known. In the current study, we show that PEA-OXA, besides being an alpha2 adrenergic receptor antagonist, also acts as a modulator at histamine H3 receptors, and report data on its effects on sensory, affective and cognitive symptoms associated with the spared nerve injury (SNI) model of neuropathic pain in mice. Treatment for 14 days with PEA-OXA after the onset of the symptoms associated with neuropathic pain resulted in the following effects: (i) allodynia was decreased; (ii) affective/cognitive impairment associated with SNI (depression, spatial, and working memories) was counteracted; (iii) long-term potentiation in vivo in the lateral entorhinal cortex-dentate gyrus (perforant pathway, LPP) was ameliorated, (iv) hippocampal glutamate, GABA, histamine, norepinephrine and dopamine level alterations after peripheral nerve injury were reversed, (v) expression level of the TH positive neurons in the Locus Coeruleus were normalized. Thus, a 16-day treatment with PEA-OXA alleviates the sensory, emotional, cognitive, electrophysiological and neurochemical alterations associated with SNI-induced neuropathic pain.

N-Substituted piperazine derivatives as potential multitarget agents acting on histamine H3 receptor and cancer resistance proteins

Taking into account that multidrug resistance (MDR) is the main cause for chemotherapeutic failure in cancer treatment, the ability of novel histamine H₃ receptor ligands to reverse the cancer MDR was evaluated, using the ABCB1 efflux pump inhibition assay in mouse MDR T-lymphoma cells. The most active compounds displayed significant cytotoxic and antiproliferative effects as well as a very potent MDR efflux pump inhibitory action, 3-5-fold stronger than that of reference inhibitor verapamil. Although these compounds possess weak antagonistic properties against histamine H₃ receptors, they are valuable pharmacological tools in the search for novel anticancer molecules. Furthermore, for the most active compounds, an insight into mechanisms of action using either, the luminescent Pgp-Glo™ Assay in vitro or docking studies to human Pgp, was performed.

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.