Synthesis and characterization of [125I]3′-(−)-iodopentazocine, a selective σ1 receptor ligand

George C. Cotzias Laboratory of Neuro-Oncology, Department of Neurology, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
European Journal of Pharmacology (Impact Factor: 2.53). 04/1997; 321(3):361-8. DOI: 10.1016/S0014-2999(96)00963-6
Source: PubMed


Pentazocine is a potent ligand at both opioid and sigma receptors, but with opposite stereoselectivities. Whereas (-)-pentazocine has high affinity for a number of opioid receptors, (+)-pentazocine labels sigma 1 receptors. Iodination of (-)-pentazocine at the 3'-position reverses its selectivity for opioid and sigma 1 receptors. 3'-(-)-Iodopentazocine competes at sigma 1 receptor binding sites with a Ki value of 8 nM, compared to approximately 40 nM for (-)-pentazocine. 3'-(-)-Iodopentazocine also has lost its affinity for opioid receptors. In contrast, iodination of (+)-pentazocine lowers its affinity at sigma 1 receptors. Synthesis of [125I]3'-(-)-iodopentazocine is readily performed with incorporations of up to 80%. Binding is of high affinity and shows the selectivity anticipated for a sigma 1 receptor-selective ligand. Exposing membranes prebound with [125I]3'-(-)-iodopentazocine to ultraviolet light can covalently couple the ligand into the membranes. Polyacrylamide gel electrophoresis reveals a major band at about 25 kDa and a minor one at about 20 kDa, indicating photolabeling of sigma 1 receptors with minor incorporation into sigma 2 sites.

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    • "Although (Ϫ)pentazocine labels ␮ and ␬ opioid binding sites with high affinity, it has only modest affinity for ␴ sites. Conversely, (ϩ)pentazocine selectivity labels ␴ 1 receptors (K i ϭ 1.8 nM) approximately 500-fold more potently than ␮ opioid sites (K i Ͼ 700 nM) and more than 30-fold more potently than ␬ 1 binding sites (Chien et al., 1997). Likewise, the ␴ ligand BD1047 shows poor affinity for opioid binding sites (K i Ͼ 1000 nM) while labeling ␴ 1 sites with very high affinity (K i ϭ 0.9 nM) (Matsumoto et al., 1995). "
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    ABSTRACT: sigma Ligands modulate opioid actions in vivo, with agonists diminishing morphine analgesia and antagonists enhancing the response. Using human BE(2)-C neuroblastoma cells that natively express opioid receptors and human embryonic kidney (HEK) cells transfected with a cloned mu opioid receptor, we now demonstrate a similar modulation of opioid function, as assessed by guanosine 5'-O-(3-[(35)S]thio)triphosphate ([(35)S]GTP gamma S) binding, by sigma(1) receptors. sigma Ligands do not compete opioid receptor binding. Administered alone, neither sigma agonists nor antagonists significantly stimulated [(35)S]GTP gamma S binding. Yet sigma receptor selective antagonists, but not agonists, shifted the EC(50) of opioid-induced stimulation of [(35)S]GTP gamma S binding by 3- to 10-fold to the left. This enhanced potency was seen without a change in the efficacy of the opioid, as assessed by the maximal stimulation of [(35)S]GTP gamma S binding. sigma(1) Receptors physically associate with mu opioid receptors, as shown by coimmunoprecipitation studies in transfected HEK cells, implying a direct interaction between the proteins. Thus, sigma receptors modulate opioid transduction without influencing opioid receptor binding. RNA interference knockdown of sigma(1) in BE(2)-C cells also potentiated mu opioid-induced stimulation of [(35)S]GTP gamma S binding. These modulatory actions are not limited to mu and delta opioid receptors. In mouse brain membrane preparations, sigma(1)-selective antagonists also potentiated both opioid receptor and muscarinic acetylcholine receptor-mediated stimulation of [(35)S]GTP gamma S binding, suggesting a broader role for sigma receptors in modulating G-protein-coupled receptor signaling.
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    ABSTRACT: We determined the effects of (+)pentazocine, a selective sigma(1) ligand, on the uptake of glycylsarcosine (Gly-Sar) in the human intestinal cell line Caco-2 which expresses the low affinity/high capacity peptide transporter PEPT1. Confluent Caco-2 cells were treated with various concentrations of (+)pentazocine for desired time (mostly 24 hr). The activity of PEPT1 was assessed by measuring the uptake of [(14)C]Gly-Sar in the presence of a H(+) gradient. (+)Pentazocine increased the uptake of [(14)C]Gly-Sar mediated by PEPT1 in a concentration- and time-dependent manner. Kinetic analyses have indicated that (+)pentazocine increased the maximal velocity (V(max)) for Gly-Sar uptake in Caco-2 cells without affecting the Michaelis-Menten constant (K(t)). In addition, semi-quantitative RT-PCR revealed that treatment of (+)pentazocine increased PEPT1 mRNA in Caco-2 cells in a concentration-dependent manner. These data suggest that sigma(1) receptor ligand (+)pentazocine up-regulates PEPT1 in Caco-2 cells at the level of increased mRNA, causing an increase in the density of the transporter protein in the cell membrane.
    Biochemical and Biophysical Research Communications 09/1999; 261(2):242-6. DOI:10.1006/bbrc.1999.1026 · 2.30 Impact Factor
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