Role of histamine H4 receptor ligands in bleomycin-induced pulmonary fibrosis.

Fibrosis of lung tissue is a disease where a chronic inflammatory process determines a pathological remodelling of lung parenchyma. The animal model obtained by intra-tracheal administration of bleomycin in C57BL/6 mice is one of the most validated murine model. Bleomycin stimulates oxidative stress and the production of pro-inflammatory mediators. Histamine H4R have recently been implicated in inflammation and immune diseases. This study was focused to investigate the effects of H4R ligands in the modulation of inflammation and in the reduction of lung fibrosis in C57BL/6 mice treated with bleomycin. C57BL/6 mice were treated with vehicle, JNJ7777120 (JNJ, selective H4R antagonist) or ST-1006 (partial H4R agonist), ST-994 (H4R neutral antagonist) and ST-1012 (inverse H4R agonist) at equimolar doses, released by micro-osmotic pumps for 21days. Airway resistance to inflation was assayed and lung samples were processed to measure malondialdehyde (TBARS); 8-hydroxy-2'-deoxyguanosine (8OHdG); myeloperoxidase (MPO); COX-2 expression and activity as markers of oxidative stress and inflammation. Fibrosis and airway remodelling were evaluated throughout transforming growth factor-ß (TGF-ß), percentage of positive Goblet cells, smooth muscle layer thickness determination. Our results indicated that JNJ, ST-994 and ST-1012 decreased inflammation and oxidative stress markers, i.e. the number of infiltrating leukocytes evaluated as lung tissue MPO, COX-2 expression and activity, TBARS and 8OHdG production. They also reduced the level of TGF-ß, a pro-fibrotic cytokine, collagen deposition, thickness of smooth muscle layer, Goblet cells hyperplasia; resulting in a decrease of airway functional impairment. The results here reported clearly demonstrated that H4R ligands have a beneficial effect in a model of lung fibrosis in the mouse, thus indicating that H4R antagonists or inverse agonists could be a novel therapeutic strategy for lung inflammatory diseases.

Drug-likeness approach of 2-aminopyrimidines as histamine H3 receptor ligands.

A small series of compounds containing derivatives of 2,4-diamino- and 2,4,6-triaminopyrimidine (compounds 2-7) was synthesized and tested for binding affinity to human histamine H3 receptors (hH3Rs) stably expressed in HEK-293 cells and human H4Rs (hH4Rs) co-expressed with Gαi2 and Gß1γ2 subunits in Sf9 cells. Working in part from the lead compound 6-(4-methylpiperazin-1-yl)-N (4)-(3-(piperidin-1-yl)propyl)pyrimidine-2,4-diamine (compound 1) with unsatisfactory affinity and selectivity to hH3Rs, our structure-activity relationship studies revealed that replacement of 4-methylpiperazino by N-benzylamine and substitution of an amine group at the 2-position of the 2-aminopyrimidine core structure with 3-piperidinopropoxyphenyl moiety as an hH3R pharmacophore resulted in N (4)-benzyl-N (2)-(4-(3-(piperidin-1-yl)propoxy)phenyl)pyrimidine-2,4-diamine (compound 5) with high hH3R affinity (k(i) =4.49 ± 1.25 nM) and H3R receptor subtype selectivity of more than 6,500×. Moreover, initial metric analyses were conducted based on their target-oriented drug-likeness for predictively quantifying lipophilicity, ligand efficiency, lipophilicity-dependent ligand efficiency, molecular size-independent efficiency, and topological molecular polar surface. As to the development of potential H3R ligands, results showed that integration of the hH3R pharmacophore in hH4R-affine structural scaffolds resulted in compounds with high hH3R affinity (4.5-650 nM), moderate to low hH4R affinity (4,500-30,000 nM), receptor subtype selectivity (ratio hH4R/hH3R; 8-6,500), and promising calculated drug-likeness properties.