Inhibition of adenylyl cyclase activity by the cholecystokinin analog SNF 9007 in neuroblastoma × glioma NG108-15 hybrid cells

The effect of the cholecystokinin_B (CCK_B) receptor-selective cholecystokinin octapeptide (CCK-8) analog SNF 9007 on forskolin-stimulated adenylyl cyclase activity in NG108-15 hybrid cells was measured. The activity of SNF 9007 was compared to the δ opioid agonists D-Pen² - D-Pen⁵-enkephalin (DPDPE, δ₁ receptor-selective) and Tyr - D-Ala - Phe - Glu - Val - Val - Gly - NH₂, (D-Ala²-deltorphin II, δ₂-receptor-selective) because SNF 9007 binds with moderate affinity to δ opioid receptors. SNF 9007 inhibited forskolin-stimulated adenylyl cyclase activity with efficacy similar to DPDPE. IC₅₀ determinations showed that D-Ala²-deltorphin II was the most potent, followed by DPDPE, then SNF 9007 (IC₅₀ values = 0.013, 0.21 and 4.8 μM, respectively). CCK-8 had no effect on adenylyl cyclase activity. The δ₁ receptor-selective antagonist 7-benzylidenenaltrexone hydrochloride (BNTX, 10 nM) had no effect on the activity of any of these agonists, but the δ₂ receptor-selective antagonist naltriben methanesulfonate (NTB, 10 nM) increased IC₅₀ values of all the agonists. Combinations of BNTX and NTB (10 nM each) increased the D-Ala²-deltorphin II IC₅₀ value 12-fold, the DPDPE IC₅₀ value 18-fold and the SNF 9007 IC₅₀ value 26-fold. The effect of the combined δ antagonists on SNF 9007 activity was different from the effect on DPDPE or D-Ala²-deltorphin II activity. These data suggest that the interaction of the CCK-8 analog SNF 9007 with opioid receptors in NG108-15 hybrid cells is different from the interaction of opioid peptides with these receptors.