Spetea Mariana, Tóth Fanni, Schütz Johannes, Otvös Ferenc, Tóth Géza, Benyhe Sandor, Borsodi Anna, Schmidhammer Helmut
Division of Pharmaceutical Chemistry, Department of Pharmacy, University of Innsbruck, Innrain 52a, A-6020 Innsbruck, Austria.
Eur J Neurosci. 2003 Jul;18(2):290-5. doi: 10.1046/j.1460-9568.2003.02744.x.
The highly potent micro -opioid receptor agonist 14-methoxymetopon (4,5alpha-epoxy-3-hydroxy-14beta-methoxy-5beta,17-dimethylmorphinan-6-one) was prepared in tritium labelled form by a catalytic dehalogenation method resulting in a specific radioactivity of 15.9 Ci/mmol. Opioid binding characteristics of [3H]14-methoxymetopon were determined using radioligand binding assay in rat brain membranes. [3H]14-Methoxymetopon specifically labelled a single class of opioid sites with affinity in low subnanomolar range (Ki = 0.43 nm) and maximal number of binding sites of 314 fmol/mg protein. Binding of [3H]14-methoxymetopon was inhibited by ligands selective for the micro -opioid receptor with high potency, while selective kappa-opioids and delta-opioids were weaker inhibitors. 14-Methoxymetopon increased guanosine-5'-O-(3-[35S]thio)-triphosphate ([35S]GTPgammaS) binding with an EC50 of 70.9 nm, thus, providing evidence for the agonist character of this ligand. The increase of [35S]GTPgammaS binding was inhibited by naloxone and selective micro -opioid antagonists, indicating a micro -opioid receptor-mediated action. [3H]14-Methoxymetopon is one of the few nonpeptide mu-opioid receptor agonists available in radiolabelled form up to now. Due to its high affinity and selectivity, high stability and extremely low nonspecific binding (<10%), this radioligand would be an important and useful tool in probing mu-opioid receptor mechanisms, as well as to promote a further understanding of the opioid system at the cellular and molecular level.
强效微阿片受体激动剂14-甲氧基美托酮（4,5α-环氧-3-羟基-14β-甲氧基-5β,17-二甲基吗啡喃-6-酮）通过催化脱卤法制备成氚标记形式，比活度为15.9 Ci/mmol。使用大鼠脑膜放射性配体结合试验测定了[3H]14-甲氧基美托酮的阿片样物质结合特性。[3H]14-甲氧基美托酮特异性标记了一类阿片样物质位点，其亲和力处于低亚纳摩尔范围（Ki = 0.43 nM），最大结合位点数为314 fmol/mg蛋白质。[3H]14-甲氧基美托酮的结合被对微阿片受体具有高选择性的配体强力抑制，而选择性κ-阿片样物质和δ-阿片样物质是较弱的抑制剂。14-甲氧基美托酮使鸟苷-5'-O-(3-[35S]硫代)-三磷酸（[35S]GTPγS）结合增加，EC50为70.9 nM，因此，为该配体的激动剂特性提供了证据。[35S]GTPγS结合的增加被纳洛酮和选择性微阿片拮抗剂抑制，表明是微阿片受体介导的作用。[3H]14-甲氧基美托酮是目前少数以放射性标记形式可得的非肽类μ-阿片受体激动剂之一。由于其高亲和力和选择性、高稳定性以及极低的非特异性结合（<10%），这种放射性配体将是探索μ-阿片受体机制以及促进在细胞和分子水平上对阿片系统的进一步理解的重要且有用的工具。
