Maristella Adami

Fragment based design of new H4 receptor-ligands with anti-inflammatory properties in vivo

Using a previously reported flexible alignment model we have designed, synthesized, and evaluated a series of compounds at the human histamine H 4 receptor (H 4R) from which 2-(4-methyl-piperazin-1-yl)-quinoxaline ( 3) was identified as a new lead structure for H 4R ligands. Exploration of the structure-activity relationship (SAR) of this scaffold led to the identification of 6,7-dichloro 3-(4-methylpiperazin-1-yl)quinoxalin-2(1 H)-one (VUF 10214, 57) and 2-benzyl-3-(4-methyl-piperazin-1-yl)quinoxaline (VUF 10148, 20) as potent H 4R ligands with nanomolar affinities. In vivo studies in the rat reveal that compound 57 has significant anti-inflammatory properties in the carrageenan-induced paw-edema model.

Gastric antisecretory role and immunohistochemical localization of cannabinoid receptors in the rat stomach

The role of cannabinoid (CB) receptors in the regulation of gastric acid secretion was investigated in the rat by means of functional experiments and by immunohistochemistry. In anaesthetized rats with lumen‐perfused stomach, the non selective CB‐receptor agonist WIN 55,212‐2 (0.30 – 4.00 μmol kg−1, i.v.) and the selective CB1‐receptor agonist HU‐210 (0.03 – 1.50 μmol kg−1, i.v.), dose‐dependently decreased the acid secretion induced by both pentagastrin (30 nmol kg−1 h−1) and 2‐deoxy‐D‐glucose (1.25 mmol kg−1, i.v.). By contrast, neither WIN 55,212‐2 (1 – 4 μmol kg−1, i.v.) nor HU‐210 (0.03 – 1.50 μmol kg−1, i.v.) did modify histamine‐induced acid secretion (20 μmol kg−1 h−1). The selective CB2‐receptor agonist JWH‐015 (3 – 10 μmol kg−1, i.v.) was ineffective. The gastric antisecretory effects of WIN 55,212‐2 and HU‐210 on pentagastrin‐induced acid secretion were prevented by the selective CB1‐receptor antagonist SR141716A (0.65 μmol kg−1, i.v.) and unaffected by the selective CB2‐receptor antagonist SR144528 (0.65 – 2 μmol kg−1, i.v.). Bilateral cervical vagotomy and ganglionic blockade with hexamethonium (10 mg kg−1, i.v., followed by continuous infusion of 10 mg kg−1 h−1) significantly reduced, but not abolished, the maximal inhibitory effect of HU‐210 (0.3 μmol kg−1, i.v.) on pentagastrin‐induced acid secretion; by contrast, pretreatment with atropine (1 mg kg−1, i.v.) did not modify the antisecretory effect of HU‐210. Immunoreactivity to the CB1 receptor was co‐localized with that of the cholinergic marker choline acetyltransferase in neural elements innervating smooth muscle, mucosa and submucosal blood vessels of rat stomach fundus, corpus and antrum. In contrast, CB2 receptor‐like immunoreactivity was not observed. These results indicate that gastric antisecretory effects of cannabinoids in the rat are mediated by suppression of vagal drive to the stomach through activation of CB1 receptors, located on pre‐ and postganglionic cholinergic pathways. However, the ineffectiveness of atropine in reducing the effect of HU‐210 suggests that the release of non cholinergic excitatory neurotransmitters may be regulated by CB1 receptors.

Discovery of Quinazolines as Histamine H4 Receptor Inverse Agonists Using a Scaffold Hopping Approach

From a series of small fragments that was designed to probe the histamine H(4) receptor (H(4)R), we previously described quinoxaline-containing fragments that were grown into high affinity H(4)R ligands in a process that was guided by pharmacophore modeling. With a scaffold hopping exercise and using the same in silico models, we now report the identification and optimization of a series of quinazoline-containing H(4)R compounds. This approach led to the discovery of 6-chloro-N-(furan-3-ylmethyl)2-(4-methylpiperazin-1-yl)quinazolin-4-amine (VUF10499, 54) and 6-chloro-2-(4-methylpiperazin-1-yl)-N-(thiophen-2-ylmethyl)quinazolin-4-amine (VUF10497, 55) as potent human H(4)R inverse agonists (pK(i) = 8.12 and 7.57, respectively). Interestingly, both compounds also possess considerable affinity for the human histamine H(1) receptor (H(1)R) and therefore represent a novel class of dual action H(1)R/H(4)R ligands, a profile that potentially leads to added therapeutic benefit. Compounds from this novel series of quinazolines are antagonists at the rat H(4)R and were found to possess anti-inflammatory properties in vivo in the rat.

Synthesis and QSAR of quinazoline sulfonamides as highly potent human histamine H4 receptor inverse agonists.

Hit optimization of the class of quinazoline containing histamine H(4) receptor (H(4)R) ligands resulted in a sulfonamide substituted analogue with high affinity for the H(4)R. This moiety leads to improved physicochemical properties and is believed to probe a distinct H(4)R binding pocket that was previously identified using pharmacophore modeling. By introducing a variety of sulfonamide substituents, the H(4)R affinity was optimized. The interaction of the new ligands, in combination with a set of previously published quinazoline compounds, was described by a QSAR equation. Pharmacological studies revealed that the sulfonamide analogues have excellent H(4)R affinity and behave as inverse agonists at the human H(4)R. In vivo evaluation of the potent 2-(6-chloro-2-(4-methylpiperazin-1-yl)quinazoline-4-amino)-N-phenylethanesulfonamide (54) (pK(i) = 8.31 +/- 0.10) revealed it to have anti-inflammatory activity in an animal model of acute inflammation.

Pharmacological characterization of the new histamine H4 receptor agonist VUF 8430

Background and purpose:  We compare the pharmacological profiles of a new histamine H4 receptor agonist 2‐(2‐guanidinoethyl)isothiourea (VUF 8430) with that of a previously described H4 receptor agonist, 4‐methylhistamine.

Pharmacology of the novel H2 antagonist famotidine : in vitro studies

The novel antiulcer drug famotidine was found to be a potent and selective inhibitor of histamine H2 receptors. Its activity on different parameters involving H2 receptors was higher than that of other compounds of the family: pA2 values were 8.33, 7.86 and 7.83 in the guinea pig atria, guinea pig papillary muscle and isolated rat gastric secretion, respectively. Apart from quantitative differences, famotidine differred from the other compounds, since it caused a competitive antagonism only at low concentrations and an unsurmountable antagonism at higher concentrations. The duration of the inhibitory action on the “in vitro” gastric secretion resembled that of cimetidine and ranitidine. Famotidine was highly effective (approximately 10 times as potent as ranitidine) also on the rat uterus (unsurmountable antagonism) and on the guinea pig gallbladder (pA2value=7.71). Famotidine was apparently devoid of non-specific effects converning the gastrointestinal motility even at very high concentrations (10−4 M). In this respect, famotidine appeared to be more selective than cimetidine and ranitidine at the H2 receptor level. The high potency, the peculiarity of the antagonism and the lack of side-effects on a number of isolated preparations, indicate this H2 antagonist as a very peculiar member of the group.

Effect of some new H2-receptor antagonists on gastrointestinal motility

Some new histamine H2-receptor antagonists were tested for their effects on gastrointestinal motility. Ranitidine was found to possess definite stimulatory effects which appeared to be connected with an interference with the cholinergic system and occurred, though in different degree, from the lower esophageal sphincter (LES) to the colon. Etintidine, on the contrary, showed a remarkable antimuscarinic effect on the LES of the rat and the guinea-pig. Cimetidine, SK&F 93479 and tiotidine were virtually ineffective whereas oxmetidine exerted a consistent inhibitory activity on both basal motility and on the contractions induced by a variety of stimulatory agents. This effect, which was completely independent of the autonomic nervous system appreared to be connected with an inhibition of the transport of calcium ions. All the above results suggest that the H2-antagonists so far available may not be absolutely selective for the H2-receptor but may be endowed with non-specific effects which could have an interest at least from a pharmacological viewpoint.

Histamine H3 Receptors Are Not Involved in the Regulation of Rat Gastric Secretion

The effects of histamine H3 receptor activation [(R)alpha-methylhistamine] and blockade (thioperamide) on rat gastric secretion were determined in vivo and in vitro. (R)alpha-Methylhistamine (0.1-5 mumol/kg i.p.) did not modify secretory volume and acidity in pylorus-ligated rats; it did not affect basal acid secretion and the secretion stimulated by histamine, pentagastrin and 2-deoxy-D-glucose in the lumen-perfused stomach of anaesthetized rats, when administered by continuous infusion (0.01-1 mumol/kg/h) or bolus injection (0.05-25 mumol/kg). In this preparation, the H3 agonist increased acid secretion at doses of 3-25 mumol/kg i.v., the effect being antagonized by famotidine. In the isolated gastric fundus from immature rats both (R)alpha-methylhistamine (0.01-10 mumol/l) and thioperamide (0.01-1 mumol/l) were totally ineffective against both spontaneous and stimulated gastric secretion. These results suggest that histamine H3 receptors are unlikely to have a role in regulating gastric acid secretion in the rat.

Strain-dependent effects of the histamine H(4) receptor antagonist JNJ7777120 in a murine model of acute skin inflammation

Abstract:  The effects of the histamine H4 receptor antagonist JNJ7777120 were evaluated in a model of acute skin inflammation induced by local application of croton oil. The influence of strain on the effect of JNJ7777120 was investigated in four different mouse strains (CD‐1, NMRI, BALB/c and C57BL/6J). In CD‐1 mice, JNJ777720 (30–100 mg/kg subcutaneously, s.c.) exerted a dose‐dependent inhibition of croton oil‐induced ear inflammation and polymorphonuclear leucocyte infiltration, as confirmed by histological evaluation of ear tissues. JNJ7777120 (30–100 mg/kg) did not reduce ear oedema in NMRI, BALB/c or C57BL/6J mice. The positive control, dexamethasone (2 mg/kg s.c.) induced significant anti‐inflammatory effects only in CD‐1 and NMRI mice. In these strains, also the histamine H1‐receptor blocker pyrilamine (30 mg/kg s.c.) significantly reduced ear oedema at 2 h after croton oil challenge, being as effective as JNJ7777120 in CD‐1 mice. Taken together, these data demonstrate that the H4 receptor antagonist JNJ7777120 may reduce acute croton oil‐induced skin inflammation as effectively as H1 receptor blockade. However, present experiments evidenced for the first time marked strain‐related differences in the JNJ7777120 pharmacological activity, which have to be carefully considered when using this ligand to characterize histamine H4 receptor functions in murine models and translating preclinical data to clinical human settings.

Gastric antisecretory effects of synthetic cannabinoids after central or peripheral administration in the rat.

Previous studies have revealed that cannabinoid (CB)-receptor agonists inhibit gastric acid secretion stimulated by indirectly acting agents, but not by histamine. Aiming to investigate whether central or peripheral mechanisms are involved, the effects of the synthetic CB-receptor agonists WIN55,212-2 and HU-210, administered either intracerebroventricularly (i.c.v.) or intravenously (i.v.) to the anaesthetized rat with lumen-perfused stomach, against gastric acid secretion induced by pentagastrin were tested. Injected i.c.v., both WIN55,212-2 (50 and 100 microg/kg) and HU-210 (25, 50 and 100 microg/kg) were ineffective on either basal secretion or acid output induced by pentagastrin (7.7 microg/kg, i.v.). By contrast, i.v. injections of WIN55,212-2 (100 and 1000 microg/kg) or HU-210 (10-100 microg/kg) significantly inhibited pentagastrin-induced acid secretion, maximal reductions being 75.70 and 82.24% for WIN55,212-2 and HU-210, respectively. The gastric antisecretory effect of HU-210 was prevented by administration of the selective CB(1)-receptor antagonist SR141716A (1000 microg/kg, i.v.). These results show that CB(1)-receptors mediating inhibition of gastric acid secretion in the rat are mainly peripherally located.