Histamine H3 Receptor Antagonists Go to Clinics

Abstract

INTRODUCTIONThe biogenic amine histamine, 2-(1H-imidazol-4-yl)-ethanamine, is produced by decarboxylation of L-histidine and is implicated in a wide range of physiological and pathophysiological functions. It is metabolised by histamine N tmethyltransferase (HMT) and mono-or diaminoxidase. Histamine is mainly acting via four distinct metabotropic histamine receptor subtypes (H 1 R-H 4 R), which have meanwhile all been cloned. Whereas antagonists for H 1 R and H 2 R subtypes have been blockbusters in therapy of allergy and ulcer, respectively, antagonists for H 3 R and H 4 R subtypes are not on the market. The recently described H 4 R seems to be involved in inflammatory and immunomodulatory processes. H 3 Rs play a central role in neurotransmission of histamine and in control of many other neurotransmitters. Several antagonists are in preclinical and some in clinical stage of development. PHARMACOLOGICAL BACKGROUND Auto-and HeteroreceptorThe H 3 R was first described in 1983 as a presynaptic autoreceptor, which mediates synthesis of histamine and inhibition of its release from histaminergic neurons in slices of rat cerebral cortex. 1) Localisation studies in rodents show a predominance in distinct regions of the central nervous system (CNS) as the H 3 R is mainly located in cerebral cortex, hippocampus, amygdala, nucleus accumbens, globus pallidus, striatum, and hypothalamus 2-5) ( Fig. 1). In addition, it is expressed in the peripheral nervous system, e.g. in gastrointestinal tract, airways and cardiovascular system. 6) Molecular aspects of the receptor, [7][8][9][10] structure-activity relationships (SAR) of ligands, [11][12][13][14][15][16][17][18][19] and pharmacology [20][21][22][23][24][25][26] have recently been resumed in many excellent reviews. This contribution focuses on the development of clinical candidates and the multifaceted potential indications targeted.In mammalian brain histaminergic neurons originate in the tuberomammillary nucleus (TMN) spreading into above mentioned brain regions, where they control histamine levels by regulation of synthesis and liberation rates 27) and modulate different neuronal systems. 28) H 3 R expression is not solely restricted to histaminergic neurons: due to its function as a heteroreceptor it can be found on colocalised neurons, and H 3 R activation modulates the release of various important neurotransmitters, i.e. dopamine, [29][30][31][32][33] acetylcholine, [34][35][36][37] norepinephrine, 38,39) serotonin, 40,41) GABA, [42][43][44] glutamate, 45) and substance P. [46][47][48] Therefore, histaminergic neurons and the cross-linkage between major neurotransmitter systems are involved in many (patho)physiological brain functions, including vigilance, memory processes, feeding behaviour and locomotor activity (Fig. 2). Interneuron cross-talk and adaptive processes seem to be important factors in H 3 Rmediated signalling. Molecular AspectsThe human histamine H 3 receptor (hH 3 R) cDNA firstly described 1999 encodes a 445 amino acid protein and belongs to the his...

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Kojic Acid Derivatives as Histamine H3 Receptor Ligands

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Histamine neuronal system as a therapeutic target for the treatment of cognitive disorders

“…Moreover, in a pilot single-blind clinical trial on 22 patients diagnosed with narco lepsy receiving a placebo for 1 week, followed by tiprolisant (BF2.649) for a second week, the Epworth sleepiness scale (ESS) score was reduced from a baseline value of 17.6 by 1.0 with the placebo (p > 0.05), and 5.9 with tiprolisant (p < 0.001) [106]. EDS, unaffected under placebo, was nearly suppressed on the last days [108]). However, there are potential therapeutic applications for H 3 R agonists as well.…”