Histamine is a multifunctional hormone that regulates smooth muscle contraction in the airways, acid secretion in the gut, and neurotransmitter release in the central nervous system through three well characterized receptor subtypes, H(1), H(2), H(3), respectively. As part of a directed effort to discover novel G-protein-coupled receptors through homology searching of genomic databases, we identified a partial clone (GPCR105) that had significant homology to the recently identified histamine H(3) receptor cDNA. Expression of the full-length human GPCR105 in cells confers the ability to bind [(3)H]histamine with high affinity (K(D) = 5 nM). GPCR105 is pharmacologically similar to the histamine H(3) receptor in that it binds many of the known H(3) agonists and antagonists, albeit with a different rank order of affinity/potency. GPCR105 does not bind (i.e., K(D) > 10 microM) all tested H(1) and H(2) receptor antagonists such as diphenhydramine, loratadine, ranitidine, and cimetidine, but has modest affinity for the H(2) receptor agonist, dimaprit (377 nM). Whereas the H(3) receptor is expressed almost exclusively in nervous tissues, GPRC105 is expressed primarily in bone marrow and eosinophils. Together, these data demonstrate that GPCR105 is a novel histamine receptor structurally and pharmacologically related to the H(3) receptor. However, its unique expression profile and physiological role suggest that GPCR105 is a fourth histamine receptor subtype (H(4)) and may be a therapeutic target for the regulation of immune function, particularly with respect to allergy and asthma.

Following the discovery of the human histamine H4 receptor, a high throughput screen of our corporate compound collection identified compound 6 as a potential lead. Investigation of the SAR resulted in the discovery of novel compounds 10e and 10l, which are the first potent and selective histamine H4 receptor antagonists to be described.

Three series of H(4) receptor ligands, derived from indoly-2-yl-(4-methyl-piperazin-1-yl)-methanones, have been synthesized and their structure-activity relationships evaluated for activity at the H(4) receptor in competitive binding and functional assays. In all cases, substitution of small lipophilic groups in the 4 and 5-positions led to increased activity in a [(3)H]histamine radiolabeled ligand competitive binding assay. In vitro metabolism and initial pharmacokinetic studies were performed on selected compounds leading to the identification of indole 8 and benzimidazole 40 as potent H(4) antagonists with the potential for further development. In addition, both 8 and 40 demonstrated efficacy in in vitro mast cell and eosinophil chemotaxis assays.

In rodents 5-hydroxytryptamine type 7 (5-HT 7 ) receptor blockade has been shown to be effective in models of depression and to increase the latency to rapid eye movement (REM) sleep and decrease REM duration. In the clinic, the REM sleep reduction observed with many antidepressants may serve as a biomarker. We report here the preclinical and clinical evaluation of a 5-HT 7 receptor antagonist, (3-(4-chlorophenyl)-1, 4,5,6,7,8-hexahydro-1-(phenylmethyl)pyrazolo [3,4-d]azepine 2-hydroxy-1,2,3-propanetricarboxylate) (JNJ-18038683). In rodents, JNJ-18038683 increased the latency to REM sleep and decreased REM duration, and this effect was maintained after repeated administration for 7 days. The compound was effective in the mouse tail suspension test. JNJ-18038683 enhanced serotonin transmission, antidepressant-like behavior, and REM sleep suppression induced by citalopram in rodents. In healthy human volunteers JNJ-18038683 prolonged REM latency and reduced REM sleep duration, demonstrating that the effect of 5-HT 7 blockade on REM sleep translated from rodents to humans. Like in rats, JNJ-18038683 enhanced REM sleep suppression induced by citalopram in humans, although a drugdrug interaction could not be ruled out. In a double-blind, active, and placebo-controlled clinical trial in 225 patients suffering from major depressive disorder, neither treatment with pharmacologically active doses of JNJ-18038683 or escitalopram separated from placebo, indicating a failed study lacking assay sensitivity. Post hoc analyses using an enrichment window strategy, where all the efficacy data from sites with an implausible high placebo response [placebo group Montgomery-Åsberg Depression Rating Scale (MADRS) Ͻ ϭ 12] and from sites with no placebo response (MADRS Ͼ ϭ 28) are removed, there was a clinically meaningful difference between JNJ-18038683 and placebo. Further clinical studies are required to characterize the potential antidepressant efficacy of JNJ-18038683.

A solution-phase convergent versus linear, divergent solid-phase synthesis of chemical libraries is illustrated enlisting the 2-fold dimerization of iminodiacetic acid diamides ultimately incorporating eight variable groups. The first dimerization is conducted with ω-alkene carboxamide derivatives of iminodiacetic acid which sets up the second dimerization conducted with the olefin metathesis reaction. This latter reaction randomizes the linking tether length adding a ninth degree of diversification suitable for the discovery of receptor dimerization antagonists and their linkage into potential receptor dimerization agonists. Unlike the divergent synthesis of libraries which is amendable to solid-phase synthesis techniques, such convergent syntheses are especially suited for solution-phase synthesis and are precluded by conventional solid-phase techniques since the combining components typically would be on mutually exclusive phases. Two mixture libraries of 476 775 and 114 783 975 compounds were prepared in five steps from four ω-alkene carboxamides and 10 or 20 amines, respectively. Deconvolution of the library mixtures by positional scanning or a complementary technique we introduce as deletion synthesis can be conducted up front for depository libraries subjected to multiple assays. For convergent dimerizations such as that illustrated herein, only deletion deconvolution can provide information on all components of the mixture including the unsymmetrical combinations.