Pharmacological characterization of the novel nonpeptide orphanin FQ/nociceptin receptor agonist Ro 64-6198: rapid and reversible desensitization of the ORL1 receptor in vitro and lack of tolerance in vivo.
The novel nonpeptide orphanin FQ/nociceptin (OFQ/N) ligand [(1S,3aS)-8-(2,3,3a,4,5,6-hexahydro-1H-phenalen-1-yl)-1-phenyl-1,3,8-triaza-spiro[4.5]decan-4-one] (Ro 64-6198) was characterized in vitro and in vivo for its agonistic potential. Ro 64-6198 was 130- to 3500-fold selective for the OFQ/N receptor (ORL1) compared with opiate receptors. In the cAMP inhibition assay, Ro 64-6198 was a full agonist at the ORL1 and a partial agonist at the mu opiate receptor. When human embryonic kidney 293 cells stably expressing the human ORL1 receptor were pre-exposed (30 min) to either OFQ/N or Ro 64-6198, the ability of both agonists to inhibit forskolin-mediated cAMP accumulation was strongly reduced, indicating a functional desensitization of the second messenger cascade. However, acidic washes of OFQ/N-exposed cells fully restored the sensitivity of the ORL1 receptor for agonists. In contrast, the cAMP response in Ro 64-6198-exposed cells remained impaired after acidic washes, suggesting sustained receptor internalization at 30 min. In agreement with this finding, the number of cell-surface ORL1 receptors was significantly reduced after Ro 64-6198 pre-exposure, and this effect could be blocked with high sucrose concentrations. When Ro 64-6198 was chronically administered to rats, no signs of tolerance to its anxiolytic-like effects were detected following 15 days of daily drug exposure. In agreement with the behavioral results, Ro 64-6198 was able to reduce brain ORL1 binding sites in both acutely and chronically treated rats. Full recovery of ORL1 binding sites was observed 24 h after Ro 64-6198 administration with a t1/2 of approximately 5.5 h. These data show that nonpeptide agonists at the ORL1 receptor have a good clinical potential as anxiolytics without causing tolerance.
Dautzenberg
F M
FM
F. Hoffmann-La Roche AG, Pharma Division, Preclinical Research, Basel, Switzerland. frank.dautzenberg@axovan.com
Wichmann
J
J
Higelin
J
J
Py-Lang
G
G
Kratzeisen
C
C
Malherbe
P
P
Kilpatrick
G J
GJ
Jenck
F
F
D001007:Anxiety / Q000523:psychology; D001831:Body Temperature / Q000187:drug effects; D001923:Brain Chemistry / Q000187:drug effects; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004361:Drug Tolerance; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology*; D007668:Kidney / Q000378:metabolism; D018847:Opioid Peptides / Q000819:agonists* / Q000235:genetics; D010147:Pain Measurement / Q000187:drug effects; D019275:Radiopharmaceuticals; D011957:Receptors, Opioid / Q000187:drug effects* / Q000235:genetics; D013141:Spiro Compounds / Q000494:pharmacology*; D014162:Transfection; D015430:Weight Gain / Q000187:drug effects; D000094942:Nociceptin Receptor; D000097629:Nociceptin
D007093:Imidazoles; D018847:Opioid Peptides; D019275:Radiopharmaceuticals; D011957:Receptors, Opioid; D013141:Spiro Compounds; D000094942:Nociceptin Receptor; D000097629:Nociceptin; C408068:Ro 64-6198; C000722283:OPRL1 protein, human