The transcription factor DeltaFosB is induced in the nucleus accumbens (NAc) and dorsal striatum by the repeated administration of drugs of abuse. Here, we investigated the role of DeltaFosB in the NAc in behavioral responses to opiates. We achieved overexpression of DeltaFosB by using a bitransgenic mouse line that inducibly expresses the protein in the NAc and dorsal striatum and by using viral-mediated gene transfer to specifically express the protein in the NAc. DeltaFosB overexpression in the NAc increased the sensitivity of the mice to the rewarding effects of morphine and led to exacerbated physical dependence, but also reduced their sensitivity to the analgesic effects of morphine and led to faster development of analgesic tolerance. The opioid peptide dynorphin seemed to be one target through which DeltaFosB produced this behavioral phenotype. Together, these experiments demonstrated that DeltaFosB in the NAc, partly through the repression of dynorphin expression, mediates several major features of opiate addiction.

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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.

This study was conducted to assess the utility of unbound brain EC 50 (EC 50,u ) as a measure of in vivo potency for centrally active drugs. Seven -opioid agonists (alfentanil, fentanyl, loperamide, methadone, meperidine, morphine, and sufentanil) were selected as model central nervous system drugs because they elicit a readily measurable central effect (antinociception) and their clinical pharmacokinetics/pharmacodynamics are well understood. Mice received an equipotent subcutaneous dose of one of the model opioids. The time course of antinociception and the serum and brain concentrations were determined. A pharmacokinetic/pharmacodynamic model was used to estimate relevant parameters. In vitro measures of opioid binding affinity (K i ) and functional activity [EC 50 for agonist stimulated guanosine 5Ј-O-(3-[35 S]thio)triphosphate binding] and relevant clinical parameters were obtained to construct in vitro-to-preclinical and preclinical-to-clinical correlations. The strongest in vitro-to-in vivo correlation was observed between K i and unbound brain EC 50,u (r 2 ϳ 0.8). A strong correlation between mouse serum and human plasma EC 50 was observed (r 2 ϭ 0.949); the correlation was improved when corrected for protein binding (r 2 ϭ 0.995). Clinical equipotent i.v. dose was only moderately related to K i . However, estimates of ED 50 and EC 50 (total serum, unbound serum, total brain, and unbound brain) were significant predictors of clinical equipotent i.v. dose; the best correlation was observed for brain EC 50,u (r 2 ϭ 0.982). For each opioid, brain equilibration half-life in mice was almost identical to the plasma effect-site equilibration half-life measured clinically. These results indicate that the mouse is a good model for opioid human brain disposition and clinical pharmacology and that superior in vitro-to-preclinical and preclinicalto-clinical correlations can be achieved with relevant unbound concentrations.In drug discovery, in vitro assays and preclinical animal studies are widely used to assess compound potency and to identify compound(s) that may have a desirable clinical response. Several options for assessing compound potency are available, including in vitro (receptor binding or functional assays) and in vivo (animal studies to determine dose-response or concentration-response relationships) protocols. In vitro binding and functional assays, by nature, are designed to estimate the intrinsic affinity or potency at the receptor of interest, whereas in vivo experiments take into account the full spectrum of pharmacokinetic and pharmacodynamic processes that ultimately determine biological response.Ideally, in vitro potency would translate to or predict in vivo potency. Often, this is the case, and significant correlations between in vivo ED 50 or EC 50 and in vitro potency have been established for a variety of therapeutic targets (Leysen et al., 1983;Visser et al., 2003). However, when there is no correlation between in vivo and in vitro potency measures, the validity of the in vitro as...

Copper(i) efficiently catalyzes the "fusion" of organic azides with terminal alkynes to produce regioselectively 1,4-disubstituted-1,2,3-triazoles.[1] The very broad scope, simple experimental conditions, and exceptional reliability of this transformation have placed it among the most reliable "stitching" reactions [2] available today. It has resulted in applications in organic synthesis, molecular biology, macromolecular chemistry, and materials science. A stepwise mechanism involving the coordination of the azide to the copper(i) acetylide through the proximal nitrogen atom, followed by formation of a (1,2,3-triazol-5-yl)copper species has been proposed.[1] This mechanism is supported by computational studies, which indicate that the activation barrier for this catalytic version of the Huisgen cycloaddition is reduced by as much as 11 kcal mol À1 , which corresponds to the experimentally observed rate acceleration of seven to eight orders of magnitude.