Failure of GPI compounds to display neurotrophic activity in vitro and in vivo

The aim of this study was to evaluate the neurotrophic and neuroprotective properties of a series of immunophilin ligands and to assess the potential involvement of FK506 Binding Protein 12 kDa (FKBP12) rotamase inhibition in this activity. Both FK506 and rapamycin induced a potent inhibition of the FKBP12 rotamase activity (pIC(50) values of 7.3 and 7.4, respectively) but only a modest inhibition was observed with 1-(3,3-dimethyl-2-oxo-pentanoyl)-pyrrolidine-2-carboxylic acid S-3-pyridin-3-yl-propyl ester (GPI 1046) (5.8), its N-oxide (5.4) and thioester (6.3) analogues. Compared to nerve growth factor, all these immunophilin ligands only induced marginal increases in neurite outgrowth of rat dissociated newborn dorsal root ganglia cells. Furthermore, systemic administration of GPI 1046 and its N-oxide and thioester analogues failed to prevent striatal dopamine depletion induced by acute or chronic i.p. treatment with 1-methyl-4-phenyl 1,2,3,6 tetrahydropyridine (MPTP). These results suggest that inhibition of FKBP12 rotamase activity is not predictive for neurotrophic and neuroprotective properties of immunophilin ligands and question their therapeutic utility in neurodegenerative diseases like Parkinson's disease.

Phosphodiesterase 4 inhibitors as airways smooth muscle relaxant agents: synthesis and biological activities of triazine derivatives

A series of triazine derivatives was synthesized. The compounds were evaluated for tracheal smooth muscle relaxant and type 4 phosphodiesterase inhibitory activities. A highly significant correlation was observed between the two effects. Two compounds exhibited potent relaxant activity (EC50: 17 and 24 nM) and might be useful for the treatment of asthma.

[Mutagenesis of the human histamine H1 receptor and design of new antihistamine agents]

The binding cavity of histamine and histamine antagonists is explored using site directed mutagenesis of the human histamine H1 receptor and the amino acids involved in ligand binding are identified. Whereas Asp107 and Phe199 are important for both agonists and antagonists, two additional amino acids (Asn198 and Trp103) are required for efficient histamine binding. The binding site of antagonists is best defined as resulting from a strong ionic bond to Asp107, an orthogonal interaction between one of the aromatic rings with Phe199, and probably a hydrophobic interaction between the second aromatic ring and the lipophilic amino acids of the upper part of TMIV and TMV. This is consistent with structure-activity data of most described antagonists.

Pharmacological and functional characterisation of the wild-type and site-directed mutants of the human H1 histamine receptor stably expressed in CHO cells

A cDNA clone for the human histamine H1 receptor was isolated from a lung cDNA library and stably expressed in CHO cells. The recombinant receptor protein present in the cell membranes, displayed the functional and binding characteristics of histamine H1 receptors. Mutation of Ser155 to Ala in the fourth transmembrane domain did not significantly change the affinity of the receptor for histamine and H1 antagonists. However, mutation of the fifth transmembrane Asn198 to Ala resulted in a dramatic decrease of the affinity for histamine binding, and for the histamine-induced polyphosphoinositides breakdown, whereas the affinity towards antagonists was not significantly modified. In addition, mutation of another fifth transmembrane amino acid, Thr194 to Ala also diminished, but to a lesser extent, the affinity for histamine. These data led us to propose a molecular model for histamine interaction with the human H1 receptor. In this model, the amide moiety of Asn198 and the hydroxyl group of Thr194 are involved in hydrogen bonding with the nitrogen atoms of the imidazole ring of histamine. Moreover, mutation of Thr194 to Ala demonstrated that this residue is responsible for the discrimination between enantiomers of cetirizine.