Duration of Action of a Broad Range of Selective κ-Opioid Receptor Antagonists Is Positively Correlated with c-Jun N-Terminal Kinase-1 Activation

The kappa-opioid receptor is a widely expressed G-protein-coupled receptor that has been implicated in biological responses to pain, stress, anxiety, and depression, and its potential as a therapeutic target in these syndromes is becoming increasingly apparent. However, the prototypical selective kappa-opioid antagonists have very long durations of action that have been attributed to c-Jun N-terminal kinase (JNK) 1 activation in vivo. To test generality of this proposed noncompetitive mechanism, we used C57BL/6 wild type mice to determine the durations of antagonist action of novel kappa-opioid receptor ligands and examined their efficacies for JNK1 activation compared with conventional competitive antagonists. Of the 12 compounds tested, 5 had long durations of action that positively correlated with JNK activation: RTI-5989-97 [(3S)-7-hydroxy-N-[(1S)-1-[(3R, 4R)-4-(3-hydroxyphenyl)-3,4-dimethyl-1-piperidinyl] methyl}-(2-methylpropyl]-2-methyl-1,2, 3,4-tetrahydro-3-isoquinolinecarboxamide], RTI-5989-194 [(3R)-7hydroxy- N-[(1S)-1-[(3R, 4R)-4-(3-hydroxyphenyl)-3,4-dimethyl-1-piperidinyl] methyl}-(2-methylbutyl]-1,2,3,4-tetrahydro-3-isoquinolinecarboxamide], RTI-5989-241 [(3R)-7-hydroxy-N-[(1S)-1-{[(3R, 4R)-4-(3-methoxyphenyl)-3,4-dimethyl-1-piperidinyl] methyl}-2methylpropyl]- 1,2,3,4-tetrahydroisoquinoline-3-carboxamide)], nor-binaltorphimine (nor-BNI); and (3R)-7-hydroxy-N-((1S)1-{[(3R, 4R)-4-(3-hydroxyphenyl)-3,4-dimethyl-1-piperidinyl] methyl}2- methylpropyl)-1,2,3,4-tetrahydro-3-isoquinolinecarboxamide (JDTic). Seven had short durations of action and did not increase phospho-JNK-ir: RTI-5989-212[(3R)-N-[(1S)-1-[(3R, 4R)-4-(3hydroxyphenyl)-3,4-dimethyl-1-piperidinyl] methyl}-(2-methylpropyl]- 7-methoxy-1,2,3,4-tetrahydroisoquinoline-3-carboxamide], RTI-5989-240 [(3R)-7-hydroxy-N-[(1S)-1-[(3R, 4R)-4-(3-hydroxyphenyl)- 3,4-dimethylpiperidin-1-yl] methyl}-(2-methylpropyl]-3-methyl- 1,2,3,4-tetrahydroisoquinoline-3-carboxamide], JSPA0658 [(S)-3-fluoro-4-(4-((2-(3,5-dimethylphenyl) pyrrolidin-1-yl) methyl) phenoxy) benzamide], JSPA071B [(S)-3-fluoro-4-(4-((2-(3, 5-bis(trifluoromethyl) phenyl) pyrrolidin-1-yl) methyl) phenoxy) benzamide]. PF-4455242 [2-methyl-N-((2'-(pyrrolidin-1-ylsulfonyl) biphenyl- 4-yl) methyl) propan-1-amine], PF-4455242 [2-methyl-N-((2'(pyrrolidin-1-ylsulfonyl) biphenyl-4-yl) methyl) propan-1-amine], FP3FBZ [(S)-3-fluoro-4-(4-((2-(3-fluorophenyl) pyrrolidin-1-yl) methyl) phenoxy) benzamide], and naloxone. After long-acting antagonist treatment, pJNK-ir did not increase in mice lacking the kappa-opioid receptor; increased pJNK-ir returned to baseline by 48 h after treatment; and a second challenge with nor-BNI 72 h after the first did not increase pJNK-ir. Long-lasting antagonism and increased phospho-JNK-ir were not seen in animals lacking the JNK1 isoform. These results support the hypothesis that the duration of action of small molecule kappa-opioid receptor antagonists in vivo is determined by their efficacy in activating JNK1 and that persistent inactivation of the kappa-receptor does not require sustained JNK activation.