Na+-dependent high affinity bindin [3H]LY515300, a 3,4-dimethyl-4-(3-hydroxyphenyl)piperidine of opioid receptor inverse agonist

Analogues of 3,4-dimethyl-4-(3-hydroxyphenyl)piperidines are high affinity inverse agonists for mu-, delta- and kappa-opioid receptors. To characterize inverse agonist binding, we synthesized a high specific activity radioligand from this series, [H-3]LY515300 (3-[1-((3-cyclohexyl-[3,4-(3) H-2])-3 (R,S)-hydroxypropyl)-3 (R),4(R)-dimethylpiperidin-4-yl]phenol). In membranes expressing cloned human opioid receptors, [H-3]LY515300 binding was saturable and exhibited low nonspecific binding. [H-3]LY515300 bound with high affinity to the mu(K-d = 0.07 nM), delta- (K-d = 0.92 nM) and kappa-(K-d = 0.45 nM) opioid receptors. High affinity [H-3]LY515300 binding to all opioid receptors was Na+-dependent, a characteristic of inverse agonists. Displacement by standard opioid compounds yielded K-i values consistent with their known opioid receptor affinities. Autoradiographic localization of specific [H-3]LY515300 binding in rat and guinea pig brain was high in areas known to express high levels of opioid (particularly mu-opioid receptor) binding sites including the caudate, nucleus accumbens, and nucleus tractus solitarius. Thus, [H-3]LY515300 is the first radiolabeled opioid receptor inverse agonist useful for the study of opioid receptors in cell lines and native tissues. (C) 2003 Elsevier B.V. All rights reserved.