Recent advances in the development of histamine H3antagonists

Mechanism of Action of Atypical Antipsychotic Drugs in Mood Disorders

Atypical antipsychotic drugs were introduced in the early 1990s. Unlike typical antipsychotics, which are effective only against positive symptoms of schizophrenia, atypical antipsychotics are effective against negative and cognitive symptoms as well. Furthermore, they are effective not only in psychotic but also in affective disorders, on their own or as adjuncts to antidepressant drugs. This review presents the neural mechanisms of currently existing atypical antipsychotics and putative antipsychotics currently being investigated in preclinical and clinical studies and how these relate to their effectiveness in mood disorders such as depression, anxiety, and post-traumatic stress disorder (PTSD). Typical antipsychotics act almost exclusively on the dopamine system. Atypical drugs, however, modulate serotonin (5-HT), norepinephrine, and/or histamine neurotransmission as well. This multimodal mechanism of action putatively underlies the beneficial effect of atypical antipsychotics in mood and anxiety disorders. Interestingly, novel experimental drugs having dual antipsychotic and antidepressant therapeutic potential, such as histamine, adenosine, and trace amine-associated receptors (TAAR) ligand, are also characterized by a multimodal stimulatory effect on central 5-HT, norepinephrine, and/or histamine transmission. The multimodal stimulatory effect on central monoamine neurotransmission may be thus primarily responsible for the combined antidepressant and antipsychotic therapeutic potential of certain central nervous system (CNS) drugs.

Progress in the development of histamine H3 receptor antagonists/inverse agonists: a patent review (2013-2017)

INTRODUCTION

Since years, ligands blocking histamine H₃ receptor (H₃R) activity (antagonists/inverse agonists) are interesting targets in the search for new cures for CNS disorders. Intensive works done by academic and pharmaceutical company researchers have led to many potent and selective H₃R antagonists/inverse agonists. Some of them have reached to clinical trials.

AREAS COVERED

Patent applications from January 2013 to September 2017 and the most important topics connected with H₃R field are analysed. Espacenet, Patentscope, Pubmed, GoogleScholar or Cochrane Library online databases were principially used to collect all the materials.

EXPERT OPINION

The research interest in histamine H₃R field is still high although the number of patent applications has decreased during the past 4 years (around 20 publications). Complexity of histamine H₃R biology e.g. many isoforms, constitutive activity, heteromerization with other receptors (dopamine D₂, D₁, adenosine A_2A) and pharmacology make not easy realization and evaluation of therapeutic potential of anti-H₃R ligands. First results from clinical trials have verified potential utility of histamine H₃R antagonist/inverse agonists in some diseases. However, more studies are necessary for better understanding of an involvement of the histaminergic system in CNS-related disorders and helping more ligands approach to clinical trials and the market. Lists of abbreviations: hAChEI - human acetylcholinesterase inhibitor; hBuChEI - human butyrylcholinesterase inhibitor; hMAO - human monoamine oxidase; MAO - monoamine oxidase.

Tetrahydroisoquinolines in therapeutics: a patent review (2010-2015)

INTRODUCTION

1,2,3,4-Tetrahydroisoquinoline (THIQ) is one of the 'privileged scaffolds', commonly found in nature. Initially, this class of compounds was known for its neurotoxicity. Later on, 1-methyl-1,2,3,4-tetrahydroisoquinoline was proved as an endogeneous Parkinsonism-preventing agent in mammals. The fused THIQs have been studied for their role as anticancer antibiotics. The US FDA approval of the trabectedin for the treatment of soft tissue sarcomas, is a milestone in the anticancer drug discovery. Areas covered: This review covers the patents on various therapeutic activities of the THIQ derivatives in the years between 2010 and 2015. Patents were collected using a thorough search of Espacenet and WIPO databases. The therapeutic areas covered include cancer, malaria, central nervous system (CNS), cardiovascular, metabolic disorders, and so on. This also includes several patents on specific THIQs of clinical importance. Expert opinion: A large number of the THIQ derivatives have been synthesised for various therapeutic activities, with noticeable success in the area of drug discovery for cancer and CNS. They may also prove to be promising candidates for various infectious diseases, such as malaria, tuberculosis, HIV-infection, HSV-infection, leishmaniasis, etc. They can also be developed as novel class of drugs for various therapeutic activities with unique mechanism of action.

International Union of Basic and Clinical Pharmacology. XCVIII. Histamine Receptors

Histamine is a developmentally highly conserved autacoid found in most vertebrate tissues. Its physiological functions are mediated by four 7-transmembrane G protein-coupled receptors (H1R, H2R, H3R, H4R) that are all targets of pharmacological intervention. The receptors display molecular heterogeneity and constitutive activity. H1R antagonists are long known antiallergic and sedating drugs, whereas the H2R was identified in the 1970s and led to the development of H2R-antagonists that revolutionized stomach ulcer treatment. The crystal structure of ligand-bound H1R has rendered it possible to design new ligands with novel properties. The H3R is an autoreceptor and heteroreceptor providing negative feedback on histaminergic and inhibition on other neurons. A block of these actions promotes waking. The H4R occurs on immuncompetent cells and the development of anti-inflammatory drugs is anticipated.

Cherry-picked ligands at histamine receptor subtypes

Histamine, a biogenic amine, is considered as a principle mediator of multiple physiological effects through binding to its H1, H2, H3, and H4 receptors (H1-H4Rs). Currently, the HRs have gained attention as important targets for the treatment of several diseases and disorders ranging from allergy to Alzheimer's disease and immune deficiency. Accordingly, medicinal chemistry studies exploring histamine-like molecules and their physicochemical properties by binding and interacting with the four HRs has led to the development of a diversity of agonists and antagonists that display selectivity for each HR subtype. An overview on H1-R4Rs and developed ligands representing some key steps in development is provided here combined with a short description of structure-activity relationships for each class. Main chemical diversities, pharmacophores, and pharmacological profiles of most innovative H1-H4R agonists and antagonists are highlighted. Therefore, this overview should support the rational choice for the optimal ligand selection based on affinity, selectivity and efficacy data in biochemical and pharmacological studies. This article is part of the Special Issue entitled 'Histamine Receptors'.

Procognitive properties of drugs with single and multitargeting H3 receptor antagonist activities

The histamine H3 receptor (H3 R) is an important modulator of numerous central control mechanisms. Novel lead optimizations for H3 R antagonists/inverse agonists involved studies of structure-activity relationships, cross-affinities, and pharmacokinetic properties of promising ligands. Blockade of inhibitory histamine H3 autoreceptors reinforces histaminergic transmission, while antagonism of H3 heteroreceptors accelerates the corticolimbic liberation of acetylcholine, norepinephrine, glutamate, dopamine, serotonin and gamma-aminobutyric acid (GABA). The H3 R positioned at numerous neurotransmission crossroads indicates therapeutic applications of small-molecule H3 R modulators in a number of psychiatric and neurodegenerative diseases with various clinical candidates available. Dual target drugs displaying H3 R antagonism/inverse agonism with inhibition of acetylcholine esterase (AChE), histamine N-methyltransferase (HMT), or serotonin transporter (SERT) are novel class of procognitive agents. Main chemical diversities, pharmacophores, and pharmacological profiles of procognitive agents acting as H3 R antagonists/inverse agonists and dual H3 R antagonists/inverse agonists with inhibiting activity on AChE, HMT, or SERT are highlighted here.

Pharmacological characterization of A-960656, a histamine H₃ receptor antagonist with efficacy in animal models of osteoarthritis and neuropathic pain

Histamine H(3) receptor antagonists have been widely reported to improve performance in preclinical models of cognition, but more recently efficacy in pain models has also been described. Here, A-960656 ((R)-2-(2-(3-(piperidin-1-yl)pyrrolidin-1-yl)benzo[d]thiazol-6-yl)pyridazin-3(2H)-one) was profiled as a new structural chemotype. A-960656 was potent in vitro in histamine H(3) receptor binding assays (rat K(i)=76 nM, human K(i)=21 nM), and exhibited functional antagonism in blocking agonist-induced [(35)S]GTPγS binding (rat H(3) K(b)=107 nM, human H(3) K(b)=22 nM), and was highly specific for H(3) receptors in broad screens for non-H(3) sites. In a spinal nerve ligation model of neuropathic pain in rat, oral doses of 1 and 3mg/kg were effective 60 min post dosing with an ED(50) of 2.17 mg/kg and a blood EC(50) of 639 ng/ml. In a model of osteoarthritis pain, oral doses of 0.1, 0.3, and 1mg/kg were effective 1h post dosing with an ED(50) of 0.52 mg/kg and a blood EC(50) of 233 ng/ml. The antinociceptive effect of A-960656 in both pain models was maintained after sub-chronic dosing up to 12 days. A-960656 had excellent rat pharmacokinetics (t(1/2)=1.9h, 84% oral bioavailability) with rapid and efficient brain penetration, and was well tolerated in CNS behavioral safety screens. In summary, A-960656 has properties well suited to probe the pharmacology of histamine H(3) receptors in pain. Its potency and efficacy in animal pain models provide support to the notion that histamine H(3) receptor antagonists are effective in attenuating nociceptive processes.

Discovery of a potent thiadiazole class of histamine h3 receptor antagonist for the treatment of diabetes

A series of novel 2-piperidinopiperidine thiadiazoles were synthesized and evaluated as new leads of histamine H3 receptor antagonists. The 4-(5-([1,4'-bipiperidin]-1'-yl)-1,3,4-thiadiazol-2-yl)-2-(pyridin-2-yl)morpholine (5u) displayed excellent potency and ex vivo receptor occupancy. Compound 5u was also evaluated in vivo for antidiabetic efficacy in STZ diet-induced obesity type 2 diabetic mice for 2 or 12 days. Non-fasting glucose levels were significantly reduced as compared with vehicle-treated mice. In addition, 5u dose dependently blocked the increase of HbA1c after 12 days of treatment.

Histamine H3 and H4 receptor affinity of branched 3-(1H-imidazol-4-yl)propyl N-alkylcarbamates

A series of imidazole-containing (non-)chiral carbamates were tested at human histamine H(3) receptor (H(3)R). All compounds displayed K(i) values below 100 nM. A trend for a stereoselectivity at human H(3)R was observed for the chiral alpha-branched ligands. Selected compounds were also tested at human histamine H(4) receptor and showed moderate to weak affinities (118-1460 nM).

A novel class of H3 antagonists derived from the natural product guided synthesis of unnatural analogs of the marine bromopyrrole alkaloid dispyrin

This Letter describes the natural product guided synthesis of unnatural analogs of the marine bromopyrrole alkaloid dispyrin, and the resulting SAR of H(3) antagonism. Multiple rounds of iterative parallel synthesis improved human H(3) IC(50) approximately 33-fold, and afforded a new class of H(3) antagonists based on the novel bromotyramine core of dispyrin.

Total synthesis and biological evaluation of the marine bromopyrrole alkaloid dispyrin: elucidation of discrete molecular targets with therapeutic potential

The first total synthesis of dispyrin, a recently reported bromopyrrole alkaloid from Agelas dispar with an unprecedented bromopyrrole tyramine motif, was achieved in three steps on a gram scale (68.4% overall). No biological activity was reported for dispyrin, so we evaluated synthetic dispyrin against>200 discrete molecular targets in radioligand binding and functional assays. Unlike most marine natural products, dispyrin (1) possesses no antibacterial or anticancer activity, but was found to be a potent ligand and antagonist of several therapeutically relevant GPCRs, the alpha1D and alpha2A adrenergic receptors and the H2 and H3 histamine receptors.