– Pituitary adenylate cyclase-activating peptide (PACAP) (6-27) is a PACAP receptor antagonist with IC50 values of 1,500, 600, and 300 nM, respectively, for rat PAC1, rat VPAC1, and human VPAC2 recombinant receptors expressed in CHO cells. It binds to PACAP receptors on SH-SY5Y and SK-N-MC human neuroblastoma and T47D human breast cancer cells (IC50s = 24.5, 106, and 105 nM, respectively) and inhibits cAMP accumulation induced by PACAP (1-38) (Kis = 457, 102, and 283 nM, respectively, in SH-SY5Y, SK-N-MC, and T47D cells).