Opioid receptor selective antagonists are important pharmacological probes in opioid receptor structural characterization and opioid agonist functional study. Thus far, a nonpeptidyl, highly selective and reversible μ opioid receptor (MOR) antagonist is unavailable. On the basis of our modeling studies, a series of novel naltrexamine derivatives have been designed and synthesized. Among them, two compounds were identified as leads based on the results of in vitro and in vivo assays. Both of them displayed high binding affinity for the MOR (K i = 0.37 and 0.55 nM). Compound 6 (NAP) showed over 700-fold selectivity for the MOR over the δ receptor (DOR) and more than 150-fold selectivity over the κ receptor (KOR). Compound 9 (NAQ) showed over 200-fold selectivity for the MOR over the DOR and approximately 50-fold selectivity over the KOR. Thus these two novel ligands will serve as leads to further develop more potent and selective antagonists for the MOR.

Page 1418. Lines 3-6 in the right column should be as follows:Molecular Design. On the basis of the molecular modeling study, two series of ligands were designed as MOR selective antagonists (Table 1). While some of these ligands have been reported previously for various purposes (e.g. control compound 8, 1 compounds 2 and 8, 2,3 and control compounds 15 and 16, 4 ), to our knowledge none of them have been discussed specifically in the literature as selective μ opioid receptor antagonists.References for the above paragraph are as follows: J. R. Synthesis and biological evaluation of alpha-and beta-6-amido derivatives of 17-cyclopropylmethyl-3,14beta-dihydroxy-4,5alpha-epoxymorphinan: potential alcohol-cessation agents.

Mu opioid receptor antagonists have clinical utility and are important research tools. To develop nonpeptide and highly selective mu opioid receptor antagonist, a series of 14-O-heterocyclic-substituted naltrexone derivatives were designed, synthesized, and evaluated. These compounds showed subnanomolar-to-nanomolar binding affinity for the mu opioid receptor. Among them, compound 1 exhibited the highest selectivity for the mu opioid receptor over the delta and kappa receptors. These results implicated an alternative 'address' domain in the extracellular loops of the mu opioid receptor. KeywordsOpioid; Mu opioid receptor; Antagonist; Naltrexone Opioid receptors were generally classified into three subtypes based on the pharmacological, behavioral, and biochemical studies. [1][2][3] Opioid antagonists have played very important roles in the study of opioid receptors. In fact, an agonist is characterized as opioid-receptor-mediated only if its effect is competitively inhibited by an opioid antagonist.4 , 5 It is important to have receptor-selective opioid antagonists as tools to identify the receptor types related to the interaction with opioid agonists.4 -6 The mu opioid receptor (MOR) is the major type that mediates opioid analgesic effects of morphine, although all three opioid receptors can be involved in analgesia. The characterization of the MOR structure-function relationship is essential because it has been found that morphine's analgesic effect, addictive properties, and other major side effects are abolished in MOR knock-out mice.7 , 8 Moreover, it has been demonstrated that the analgesic effects and the adverse side effects (including addiction and abuse liability) of morphine are primarily due to its interaction with the MOR.4 In fact, naltrexone, an opioid antagonist with moderate selectivity for the MOR, has been shown to block relapse and curb drug craving in post-dependent opiate addicts.9 , 10 Recent research results also indicate that MOR antagonists can be used in the treatment of obesity, psychosis and Parkinson's disease.11 Furthermore, highly selective MOR antagonists can be used as probes to characterize the MOR-binding pocket. Yet the lack of a non-peptidyl, highly selective, and potent MOR antagonist limits our understanding of the structure-function relationship of the MOR, the interaction of non-peptidyl MOR agonists with the receptor, and more specifically, the activation mechanism of the receptor related to its role in drug abuse and addiction.Schwyzer et al. proposed the 'message-address' concept in his analysis of the structure-activity relationship of ACTH, adrenocorticotropic hormone, and related hormones.12 By applying the 'message-address' concept, highly selective non-peptide antagonists for the kappa opioid receptor (KOR) (e.g., norbinaltorphimine (norBNI) and 5′-guanidinonaltrindole (GNTI)),13 , 14 and for the delta opioid receptor (DOR) (e.g., naltrindole (NTI))15 were designed and synthesized several years ago (Fig. 1). Thus far no potent and highly selective antagon...

Prostaglandin E2 (PGE2) mediates many effects of the midcycle luteinizing hormone (LH) surge within the periovulatory follicle. Differential expression of the four PGE2 (EP) receptors may contribute to the specialized functions of each granulosa cell subpopulation. To determine if EP receptors are differentially expressed in granulosa cells, monkeys received gonadotropins to stimulate ovarian follicular development. Periovulatory events were initiated with human chorionic gonadotropin (hCG); granulosa cells and whole ovaries were collected before (0 h) and after (24-36 h) hCG to span the 40-h primate periovulatory interval. EP receptor mRNA and protein levels were quantified in granulosa cell subpopulations. Cumulus cells expressed higher levels of EP2 and EP3 mRNA compared with mural cells 36 h after hCG. Cumulus cell EP2 and EP3 protein levels also increased between 0 and 36 h after hCG. Overall, mural granulosa cells expressed low levels of EP1 protein at 0 h and higher levels 24-36 h after hCG. However, EP1 protein levels were higher in granulosa cells away from the follicle apex compared with apex cells 36 h after hCG. Higher levels of PAI-1 protein were measured in nonapex cells, consistent with a previous study showing EP1-stimulated PAI-1 protein expression in monkey granulosa cells. EP4 protein levels were low in all subpopulations. In summary, cumulus cells likely respond to PGE2 via EP2 and EP3, whereas PGE2 controls rupture of a specific region of the follicle via EP1. Therefore, differential expression of EP receptors may permit each granulosa cell subpopulation to generate a unique response to PGE2 during the process of ovulation.

Based on a mu opioid receptor (MOR) homology model and the “isosterism” concept, three generations of 14-heteroaromatically substituted naltrexone derivatives were designed, synthesized, and evaluated as potential MOR selective ligands. The first generation ligands appeared to be MOR selective, whereas the second and the third generation ones showed MOR/kappa opioid receptor (KOR) dual selectivity. Docking of ligands 2 (MOR selective) and 10 (MOR/KOR dual selective) to the three opioid receptor crystal structures revealed a non-conserved residue facilitated “hydrogen bonding network” that could be responsible for their distinctive selectivity profiles. The MOR/KOR dual selective ligand 10 showed no agonism and acted as a potent antagonist in the tail flick assay. It also produced less severe opioid withdrawal symptoms than naloxone in morphine dependent mice. In conclusion, ligand 10 may serve as a novel lead compound to develop MOR/KOR dual selective ligands, which might possess unique therapeutic value for opioid addiction treatment.