A cell-based, high-throughput homogeneous time-resolved fluorescence assay for the screening of potential κ-opioid...

The aim of this study was to identify κ-opioid receptor (KOR) agonists from a library of 80 000 small-molecule compounds and provide the experimental basis for the development of new analgesic candidates.

The cell-based, high-throughput screen for human KOR agonists was based on the LANCE cAMP assay. Preliminary structure-activity relationship (SAR) analysis was applied according to the compounds' structures. An acetic acid twisting experiment was used to verify the pharmacodynamics.

In total, 31 compounds were identified as KOR agonists after preliminary and secondary screening. Of these compounds, five demonstrated significant KOR-stimulating activity that was comparable to U-50,488, a selective KOR agonist. The EC50 values for I-7, I-8, I-10, II-5, and II-8 were 13.34 ± 1.65, 14.01 ± 1.84, 9.57 ± 0.19, 14.94 ± 0.64, and 8.74 ± 0.72 nmol/L, respectively. Based on SAR studies, the stimulating activity of compounds with 5-phenyl-7-(trifluoromethyl)-4,5,6,7-tetrahydropyrazolo [1, 5-a] pyrimidine (group I) and 3,4-dimethoxy-N-(2-oxoethyl)-N-p-tolylbenzenesulfonamide (group II) parent structures were higher than the compound with a 5-hydroxy-2-methylbenzofuran-3-carboxylic acid (group III) parent structure. Pharmacodynamic experiments indicated that 20-40 μg/kg ip of compounds I-10 and II-8 significantly decreased the number of writhes induced by acetic acid; this finding is consistent with the SAR studies. Furthermore, the analgesic effects of compounds I-10 and II-8 were significantly antagonized in the presence of the selective KOR antagonist nor-BNI.

These findings collectively indicate that compounds I-10 and II-8 exhibit significant analgesic activities, providing evidence, at least in part, for their clinical application as new analgesic drugs.