Synthesis, conformational analysis and biological activity of cyclic analogs of the octadecaneuropeptide ODN. Design of a potent endozepine antagonist.
The octadecaneuropeptide (ODN; QATVGDVNTDRPGLLDLK) and its C-terminal octapeptide (OP; RPGLLDLK), which exert anxiogenic activity, have been previously shown to increase intracellular calcium concentration ([Ca2+]i) in cultured rat astrocytes through activation of a metabotropic receptor positively coupled to phospholipase C. It has also been found that the [d-Leu5]OP analog possesses a weak antagonistic activity. The aim of the present study was to synthesize and characterize cyclic analogs of OP and [d-Leu5]OP. On-resin homodetic backbone cyclization of OP yielded an analog, cyclo1-8 OP, which was three times more potent and 1.4-times more efficacious than OP to increase [Ca2+]i in cultured rat astrocytes. Cyclo1-8 OP also mimicked the effect of both OP and ODN on polyphosphoinositide turnover. Conversely, the cyclo1-8 [d-Leu5]OP analog was totally devoid of agonistic activity but suppressed the effect of OP and ODN on [Ca2+]i and phosphoinositide metabolism in astrocytes. The structure of these cyclic analogs has been determined by two-dimensional 1H-NMR and molecular dynamics. Cyclo1-8 OP exhibited a single conformation characterized by a gamma turn comprising residues Pro2-Leu4 and a type III beta turn encompassing residues Leu5-Lys8. Cyclo1-8 [d-Leu5]OP was present as two equimolar conformers resulting from cis/trans isomerization of the Arg-Pro peptide bond. These pharmacological and structural data should prove useful for the rational design of non peptidic ODN analogs.
Leprince
J
J
Institut Fédératif de Recherches Multidisciplinaires sur les Peptides (IFRMP 23), Laboratoire de Neuroendocrinologie Cellulaire et Moléculaire, CNRS, Université de Rouen, Mont-Saint-Aignan, France.
Oulyadi
H
H
Vaudry
D
D
Masmoudi
O
O
Gandolfo
P
P
Patte
C
C
Costentin
J
J
Fauchère
J L
JL
Davoust
D
D
Vaudry
H
H
Tonon
M C
MC
D000595:Amino Acid Sequence; D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects; D002478:Cells, Cultured; D026261:Diazepam Binding Inhibitor / Q000037:antagonists & inhibitors*; D015195:Drug Design; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009479:Neuropeptides / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology*; D010446:Peptide Fragments; D010716:Phosphatidylinositols / Q000378:metabolism; D011487:Protein Conformation; D051381:Rats; D013816:Thermodynamics
D026261:Diazepam Binding Inhibitor; D009479:Neuropeptides; D010446:Peptide Fragments; D010716:Phosphatidylinositols; C067529:diazepam binding inhibitor (33-50)