title: H-D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2: a potent and selective antagonist opioid receptors.
abstract: H-D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP) exhibited high affinity (IC50 = 2.80 nM) in displacing [3H]naloxone binding (nH = 0.89 +/- 0.1) and showed an exceptional selectivity for mu opioid receptors with an IC50(DPDPE)/IC50(naloxone) ratio of 4,840, while it displayed very low affinity for somatostatin receptors (IC50 = 22,700 nM) in rat brain binding assays. [3H]CTOP was recently custom synthesized (spec. act.: 84 Ci/mmol) and evaluated for its in vitro binding properties towards the mu opioid receptors in rat brain membrane preparations. Association and dissociation of [3H]CTOP binding to mu opioid receptors were rapid at 25 degrees C with a kinetic Kd value of 0.67 nM. Saturation experiments gave apparent Kd value of 1.11 nM and Bmax value of 136 +/- 13 fmol/mg prot at 25 degrees C. Specific [3H]CTOP binding was inhibited by a number of different opioid and opiate ligands. Among them, putative mu opioid receptor-specific ligands, such as naloxone, naltrexone and CTOP inhibited the binding with high affinity, while delta opioid receptor-specific compounds or non-opioid drugs inhibited specific [3H]CTOP binding with low affinity or they were ineffective.
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism*; D020881:Enkephalin, D-Penicillamine (2,5)-; D004745:Enkephalins / Q000378:metabolism; D007700:Kinetics; D009270:Naloxone / Q000378:metabolism; D051381:Rats; D011957:Receptors, Opioid / Q000187:drug effects* / Q000378:metabolism; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; D013004:Somatostatin / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D004745:Enkephalins; D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; C049352:phenylalanyl-cyclo(cysteinyltyrosyl-tryptophyl-ornithyl-threonyl-penicillamine)threoninamide; D009270:Naloxone; D013004:Somatostatin; D020881:Enkephalin, D-Penicillamine (2,5)-