Novel potent (dihydro)benzofuranyl piperazines as human histamine receptor ligands - Functional characterization and modeling studies on H3 and H4 receptors

Opportunities and challenges in the therapeutic exploitation of histamine and histamine receptor pharmacology in inflammation-driven disorders

Inflammation-driven diseases encompass a wide array of pathological conditions characterised by immune system dysregulation leading to tissue damage and dysfunction. Among the myriad of mediators involved in the regulation of inflammation, histamine has emerged as a key modulatory player. Histamine elicits its actions through four rhodopsin-like G-protein-coupled receptors (GPCRs), named chronologically in order of discovery as histamine H1, H2, H3 and H4 receptors (H1-4R). The relatively low affinity H1R and H2R play pivotal roles in mediating allergic inflammation and gastric acid secretion, respectively, whereas the high affinity H3R and H4R are primarily linked to neurotransmission and immunomodulation, respectively. Importantly, however, besides the H4R, both H1R and H2R are also crucial in driving immune responses, the H2R tending to promote yet ill-defined and unexploited suppressive, protective and/or resolving processes. The modulatory action of histamine via its receptors on inflammatory cells is described in detail. The potential therapeutic value of the most recently discovered H4R in inflammatory disorders is illustrated via a selection of preclinical models. The clinical trials with antagonists of this receptor are discussed and possible reasons for their lack of success described.

Therapeutic potential of LINS01 histamine H3 receptor antagonists as antineoplastic agents for triple negative breast cancer

The aims of this work were to evaluate the expression of histamine H3 receptor (H3R) in triple negative breast cancer (TNBC) samples and to investigate the antitumoral efficacy and safety of the LINS01 series of H3R antagonists, through in silico, in vitro, and in vivo approaches. Antitumor activity of LINS01009, LINS01010, LINS01022, LINS01023 was assayed in vitro in 4T1 and MDA-MB-231 TNBC cells (0.01-100 μM), and in vivo in 4T1 tumors orthotopically established in BALB/c mice (1 or 20 mg/kg). Additionally, H3R expression was assessed in 50 human TNBC samples. We have described a higher H3R mRNA expression in basal-like/TNBC tumors vs. matched normal tissue using TCGA Pan-Cancer Atlas data, and a higher H3R expression in human tumor samples vs. peritumoral tissue evidenced by immunohistochemistry associated with poorer survival. Furthermore, while all the essayed compounds showed antitumoral properties, LINS01022 and LINS01023 exhibited the most potent antiproliferative effects by: i) inducing cell apoptosis and suppressing cell migration in 4T1 and MDA-MB-231 TNBC cells, and ii) inhibiting cell growth in paclitaxel-resistant 4T1 cells (potentiating the paclitaxel antiproliferative effect). Moreover, 20 mg/kg LINS01022 reduced tumor size in 4T1 tumor-bearing mice, exhibiting a safe toxicological profile and potential for druggability estimated by ADME calculations. We conclude that the H3R is involved in the regulation of TNBC progression, offering promising therapeutic potential for the novel LINS01 series of H3R antagonists.

Neurotoxicity Assessment of 1-[(2,3-Dihydro-1-Benzofuran-2-yl)Methyl]Piperazine (LINS01 Series) Derivatives and their Protective Effect on Cocaine-Induced Neurotoxicity Model in SH-SY5Y Cell Culture

Excessive levels of dopamine in the synaptic cleft, induced by cocaine for example, activates dopaminergic receptors, mainly D₁R, D₂R, and D₃R subtypes, contributing to neurotoxic effects. New synthetic 1-[(2,3-dihydro-1-benzofuran-2-yl)methyl]piperazine derivatives (the LINS01 compounds), designed as histaminergic receptor (H₃R) ligands, are also dopaminergic receptor ligands, mainly D₂R and D₃R. This study aims to evaluate the neurotoxicity of these new synthetic LINS01 compounds (LINS01003, LINS01004, LINS01011, and LINS01018), as well as to investigate their protective potential on a cocaine model of dopamine-induced neurotoxicity using SH-SY5Y cell line culture. Neurotoxicity was assessed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), lactate dehydrogenase (LDH), and automated cell counting with fluorescent dyes (acridyl orange and propidium iodide) assays. Concentration-response curves (CRCs) were performed for all LINS compounds and cocaine using MTT assay. The results show that LINS series did not decrease cell viability after 48h of exposure-except for 100 µM LINS01018, which was discontinued from the study. Likewise, MTT, LDH, and fluorescent dyes staining showed no difference is cell viability for LINS compounds at 10 µM. When incubated with 2.5 mM cocaine (lethal concentration 50) for 48h, 10 µM of each LINS compound, metoclopramide (D₂R antagonist) and haloperidol (D₂R/D₃R antagonist), ameliorated cocaine-induced neurotoxicity. However, only metoclopramide, haloperidol, and LINS01011 compound significantly decreased LDH released in the culture medium, suggesting that this new synthetic compound presents a more robust effect. This preliminary in vitro neurotoxicity study suggests that LINS01 compounds are not neurotoxic, and that they play a promising role in preventing cocaine-induced neurotoxicity.

Evaluation of the Histamine H3 Receptor Antagonists from LINS01 Series as Cholinesterases Inhibitors - Enzymatic and Modeling Studies

Histamine is involved in several CNS processes including cognition. In the last years, H₃ receptor (H₃ R) antagonists have been widely explored for their potential on dementias and other cognitive dysfunctions, and the cooperative role between histamine and acetylcholine neurotransmissions on cognitive processes is widely known in literature. This motivated us to assess the potential of 1-[(2,3-dihydrobenzofuran-1-yl)methyl]piperazines (LINS01 compounds) as inhibitors of cholinesterases, and thus this work presents the inhibitory effect of such compounds against acetyl (AChE) and butyrylcholinesterase (BChE). A set of 16 selected compounds were evaluated, being compounds 2d and 2e the most potent inhibitors of both cholinesterases (IC₅₀ 13.2 - 33.9 μM) by competitive mechanism, as indicated by the kinetic assays. Molecular docking simulations suggested that the allylpiperazine and dihydrobenzofuran motifs present in these compounds are important to perform π-interactions with key tryptophan residues from the enzymes, increasing their affinity for both H₃ R and cholinesterases. Metric analysis support that compound 2d (LINS01022) should be highlighted due to its balanced lipophilicity (ClogP 2.35) and efficiency (LE 0.32) as AChE inhibitor. The results add important information to future design of dual H₃ R-cholinesterases ligands.

Histamine H3 and H4 receptors modulate Parkinson's disease induced brain pathology. Neuroprotective effects of nanowired BF-2649 and clobenpropit with anti-histamine-antibody therapy

Military personnel deployed in combat operations are highly prone to develop Parkinson's disease (PD) in later lives. PD largely involves dopaminergic pathways with hallmarks of increased alpha synuclein (ASNC), and phosphorylated tau (p-tau) in the cerebrospinal fluid (CSF) precipitating brain pathology. However, increased histaminergic nerve fibers in substantia nigra pars Compacta (SNpc), striatum (STr) and caudate putamen (CP) associated with upregulation of Histamine H3 receptors and downregulation of H4 receptors in human cases of PD is observed in postmortem cases. These findings indicate that modulation of histamine H3 and H4 receptors and/or histaminergic transmission may induce neuroprotection in PD induced brain pathology. In this review effects of a potent histaminergic H3 receptor inverse agonist BF-2549 or clobenpropit (CLBPT) partial histamine H4 agonist with H3 receptor antagonist, in association with monoclonal anti-histamine antibodies (AHmAb) in PD brain pathology is discussed based on our own observations. Our investigation shows that chronic administration of conventional or TiO₂ nanowired BF 2649 (1mg/kg, i.p.) or CLBPT (1mg/kg, i.p.) once daily for 1 week together with nanowired delivery of HAmAb (25μL) significantly thwarted ASNC and p-tau levels in the SNpC and STr and reduced PD induced brain pathology. These observations are the first to show the involvement of histamine receptors in PD and opens new avenues for the development of novel drug strategies in clinical strategies for PD, not reported earlier.

Histamine H3 receptor and cholinesterases as synergistic targets for cognitive decline: Strategies to the rational design of multitarget ligands

The role of histamine and acetylcholine in cognitive functions suggests that compounds able to increase both histaminergic and cholinergic neurotransmissions in the brain should be considered as promising therapeutic options. For this purpose, dual inhibitors of histamine H₃ receptors (H₃ R) and cholinesterases (ChEs) have been designed and assessed. In this context, this paper reviews the strategies used to obtain dual H₃ R/ChEs ligands using multitarget design approaches. Hybrid compounds designed by linking tacrine or flavonoid motifs to H₃ R antagonists were obtained with high affinity for both targets, and compounds designed by merging the H₃ R antagonist pharmacophore with known anticholinesterase molecules were also reported. These reports strongly suggest that key modifications in the lipophilic region (including a second basic group) seem to be a strategy to reach novel compounds, allied with longer linker groups to a basic region. Some compounds have already demonstrated efficacy in memory models, although the pharmacokinetic and toxicity profile should be considered when designing further compounds. In conclusion, the key features to be considered when designing novel H₃ R/ChEs inhibitors with improved pharmacological profile were herein summarized.

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.