Synthesis of 7,9-diazabicyclo[4.2.2]decanes as conformationally restricted κ receptor agonists: Fine tuning of the dihedral angle of the ethylenediamine pharmacophore

Hazards of Using Masking Protocols When Performing Ligand Binding Assays: Lessons From the Sigma-1 and Sigma-2 Receptors

Sigma-1 and sigma-2 receptors are emerging therapeutic targets. Although the molecular identity of the sigma-2 receptor has recently been determined, receptor quantitation has used, and continues to use, the sigma-1 selective agents (+) pentazocine or dextrallorphan to mask the sigma-1 receptor in radioligand binding assays. Here, we have assessed the suitability of currently established saturation and competition binding isotherm assays that are used to quantify parameters of the sigma-2 receptor. We show that whilst the sigma-1 receptor mask (+) pentazocine has low affinity for the sigma-2 receptor (K_i 406 nM), it can effectively compete at this site with [³H] di-O-tolyl guanidine (DTG) at the concentrations frequently used to mask the sigma-1 receptor (100 nM and 1 µM). This competition influences the apparent affinity of DTG and other ligands tested in this system. A more troublesome issue is that DTG can displace (+) pentazocine from the sigma-1 receptor, rendering it partly unmasked. Indeed, commonly used concentrations of (+) pentazocine, 100 nM and 1 µM, allowed 37 and 11% respectively of sigma-1 receptors to be bound by DTG (300 nM), which could result in an overestimation of sigma-2 receptor numbers in assays where sigma-1 receptors are also present. Similarly, modelled data for 1 µM dextrallorphan show that only 71–86% of sigma-1 receptors would be masked in the presence of 300 nM DTG. Therefore, the use of dextrallorphan as a masking agent would also lead to the overestimation of sigma-2 receptors in systems where sigma-1 receptors are present. These data highlight the dangers of using masking agents in radioligand binding studies and we strongly recommend that currently used masking protocols are not used in the study of sigma-2 receptors. In order to overcome these problems, we recommend the use of a cell line apparently devoid of sigma-1 receptors [e.g., MCF7 (ATCC HTB-22)] in the absence of any masking agent when determining the affinity of agents for the sigma-2 receptor. In addition, assessing the relative levels of sigma-1 and sigma-2 receptors can be achieved using [³H] DTG saturation binding followed by two-site analysis of (+) pentazocine competition binding with [³H] DTG.

(+)-and (-)-Phenazocine enantiomers: Evaluation of their dual opioid agonist/σ1 antagonist properties and antinociceptive effects

cis-N-Substituted N-normetazocine enantiomers possess peculiar pharmacological profiles. Indeed, dextro enantiomers bind with high affinity σ₁ receptor while opposite enantiomers bind opioid receptors. In spite of their stereochemistry, cis-N-2-phenylethyl N-normetazocine (phenazocine) enantiomers showed mixed opioid/σ₁ receptor profiles and a significant in vivo analgesia. To the best of our knowledge, there is no information available regarding the evaluation of σ₁ pharmacological profile in the antinociceptive effects of (+)- and (-)-phenazocine. Therefore, the present study was designed to ascertain this component by in vitro and in vivo studies. In particular, we tested the σ₁ affinity of both enantiomers by a predictive binding assay in absence or presence of phenytoin (DPH). Our results showed that DPH (1 mM) did not increase the σ₁ receptor affinity of (+)-and (-)-phenazocine (K_i = 3.8 ± 0.4 nM, K_i = 85 ± 2.0 nM, respectively) suggesting a σ₁ antagonist profile of both enantiomers. This σ₁ antagonistic component of two phenazocine enantiomers was corroborated by in vivo studies in which the selective σ₁ receptor agonist PRE-084, was able to unmask their σ₁ antagonistic component associated with the opioid activity. The σ₁ antagonistic component of (+)- and (-)-phenazocine may justify their analgesic activity and it suggests that they may constitute useful lead compounds to develop new ligands with this dual activity.

Endogenous opiates and behavior: 2011

This paper is the thirty-fourth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2011 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration (Section 16); and immunological responses (Section 17).