Preclinical pharmacology of AZD2327: a highly selective agonist of the δ-opioid receptor.

In the present article, we summarize the preclinical pharmacology of 4-{(R)-(3-aminophenyl)[4-(4-fluorobenzyl)-piperazin-1-yl]methyl}-N,N-diethylbenzamide (AZD2327), a highly potent and selective agonist of the δ-opioid receptor. AZD2327 binds with sub-nanomolar affinity to the human opioid receptor (K(i) = 0.49 and 0.75 nM at the C27 and F27 isoforms, respectively) and is highly selective (>1000-fold) over the human µ- and κ-opioid receptor subtypes as well as >130 other receptors and channels. In functional assays, AZD2327 shows full agonism at human δ-opioid receptors ([(35)S]GTPγ EC(50) = 24 and 9.2 nM at C27 and F27 isoforms, respectively) and also at the rat and mouse δ-opioid receptors. AZD2327 is active in a wide range of models predictive of anxiolytic activity, including a modified Geller-Seifter conflict test and social interaction test, as well as in antidepressant models, including learned helplessness. In animals implanted with microdialysis probes and then given an acute stressor by pairing electric shock delivery with a flashing light, there is an increase in norepinephrine release into the prefrontal cortex associated with this acute anxiety state. Both the benzodiazepine anxiolytic standard diazepam and AZD2327 blocked this norepinephrine release equally well, and there was no evidence of tolerance to these effects of AZD2327. Overall, these data support the role of the δ-opioid receptor in the regulation of mood, and data suggest that AZD2327 may possess unique antidepressant and anxiolytic activities that could make a novel contribution to the pharmacotherapy of psychiatric disorders.

Novel C-terminus modifications of the Dmt-Tic motif: a new class of dipeptide analogues showing altered pharmacological profiles toward the opioid receptors.

The design, synthesis and pharmacological evaluation of a novel class of Dmt-Tic dipeptide analogues are described. These resulting analogues bearing different C-terminal functionalities were found to bind to the human delta receptor with high affinity. One specific class of dipeptides bearing urea/thiourea functionalities showed partial to full activation of the delta receptor. Several dipeptides also showed good binding affinities with full activation of the human kappa receptor, a novel property for those ligands.

Development of a photolabile ligand for the endothelin-A receptor of endothelin.

Actions of endothelin (ET) are usually mediated through the so-called endothelin-A or -B (ET(A) or ET(B))-receptors. As part of our ongoing research program, we are studying the characterization of the ET(A)-receptor using specific photolabile ligands. Starting with the ET(A)-specific antagonist TTA-386 as a leading compound we developed new ET(A)-specific antagonists containing the photolabile amino acid, p-benzoyl-phenylalanine (Bpa). Following a Bpa peptide scan, with either the L- or D-isomer, we found that D-phenylalanine-6 of TTA-386 can be substituted with either L- or D-Bpa and gives analogs showing antagonistic properties, in an ET(A)-receptor preparation (rat aorta), very similar to those of TTA-386 itself. No agonistic or antagonistic properties were measured with these derivatives in an ET(B) pharmacological preparation (guinea pig lung parenchyma). Thus, these new ligands appear as very promising probes for the characterization of the ET(A)-receptor.

Development of p-benzoylbenzoylated [N,C,rANP(1-28)]pBNP32 (pBNP1) derivatives and affinity photolabeling of the bovine NPR-A receptor.

Two Nalpha-benzophenone-substituted photoprobes, derived from the high affinity NPR-A chimeric agonist [N, C, rANP(1-28)]pBNP32 (pBNP1) were assembled by solid-phase peptide synthesis. [Nalpha-p-benzoylbenzoyl, Tyr2]pBNP1 (probe A), and [Nalpha-p-benzoylbenzoyl, Tyr18]pBNP1 (probe B) were synthesized and their affinity was tested on bovine zona glomerulosa membrane preparations. Both were found to exert ANP-type high affinities (Kd = 20 pM) with Kd of 10 pM and 30 pM for probe A, and probe B, respectively. Photolabeling of NPR-A with both analogs cross-linked specifically the 130 kDa monomeric NPR-A. The maximal irreversible ligand incorporations were estimated at 18% and 41% for probe A, and probe B, respectively. These results show that the N-terminus of the chimeric compound can be acylated with a large chemical function, such as the benzophenone moiety, without loosing its affinity for the NPR-A receptor. Furthermore, Leu2 or Leu18 can be substituted with tyrosine without disturbing the binding capacity of the ligand. Finally, it appears that the pBNP1 N-terminus is close to the receptor structure as irreversible incorporation is observed after photolabeling.