Effect of chronic treatment of ohmefentanyl stereoisomers on cyclic AMP formation in Sf9 insect cells expressing human μ-opioid receptors

Abstract

The binding affinity of ohmefentanyl stereoisomers for μ-opioid receptors and the effect of chronic ohmefentanyl stereoisomers pretreatments on intracellular cAMP formation were investigated in Sf9 insect cells expressing human μ-opioid receptors (Sf9-μ cells). Competitive assay of [ 3H]ohmefentanyl binding revealed that these isomers had high affinity for μ-opioid receptors in Sf9-μ cells. Isomer F9204 had the highest affinity for μ-opioid receptors with the K i value of 1.66 ± 0.28 nM. After pretreated Sf9-μ cells with increasing concentrations of these isomers for 6 h, addition of naloxone (1 μM) precipitated an overshoot of foskolin-stimulated cAMP accumulation. The ability of these isomers to induce cAMP overshoot differed greatly with the order of F9202 > F9205 > F9208 > F9206 > F9204 > F9207. Of these isomers, F9202 was 2.7-fold less potent than F9204 in receptor binding affinity, but 71.5-fold more potent in ability to induce cAMP overshoot. These results suggested that there was a significant stereo-structural difference among ohmefentanyl stereoisomers in ability to induce naloxone-precipitated cAMP overshoot in Sf9-μ cells.