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

The effect of the cholecystokininB (CCKB) 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 delta opioid agonists D-Pen2-D-Pen5-enkephalin (DPDPE, delta 1 receptor-selective) and Tyr-D-Ala-Phe-Glu-Val-Val-Gly-NH2, (D-Ala2-deltorphin II, delta 2-receptor-selective) because SNF 9007 binds with moderate affinity to delta 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 microM, respectively). CCK-8 had no effect on adenylyl cyclase activity. The delta 1 receptor-selective antagonist 7-benzylidenenaltrexone hydrochloride (BNTX, 10 nM) had no effect on the activity of any of these agonists, but the delta 2 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 delta 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.