RT Journal Article SR Electronic T1 Creation of a Selective Antagonist and Agonist of the Rat VPAC1 Receptor Using a Combinatorial Approach with Vasoactive Intestinal Peptide 6–23 as Template JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 1035 OP 1041 DO 10.1124/mol.58.5.1035 VO 58 IS 5 A1 Jeppe Wegener Tams A1 Rikke Malene Jørgensen A1 Arne Holm A1 Jan Fahrenkrug YR 2000 UL http://molpharm.aspetjournals.org/content/58/5/1035.abstract AB We have used combinatorial chemistry with amino acid mixtures (X) at positions 6 to 23 in vasoactive intestinal peptide (VIP) to optimize binding affinity and selectivity to the rat VPAC1 receptor. The most efficient amino acid replacement was a substitution of alanine at position 18 to diphenylalanine (Dip), increasing the displacement efficiency of 125I-VIP by 370-fold. The [Dip18]VIP(6–23) was subsequently used to find a second replacement, employing the same approach. Tyrosine at position 9 was selected and the resulting [Tyr9,Dip18]VIP(6–23) analog has aK i value of 90 nM. This analog was unable to stimulate cAMP production at 10−6 M but was able to inhibit VIP-induced cAMP stimulation (K b = 79 nM). TheK i values of [Tyr9,Dip18]VIP(6–23) using the rat VPAC2 and PAC1 receptors were 3,000 nM and >10,000 nM, respectively. Thus, [Tyr9,Dip18]VIP(6–23) is a selective VPAC1 receptor antagonist. The C-terminally extended form, [Tyr9,Dip18]VIP(6–28), displays improved antagonistic properties having a K i andK b values of 18 nM and 16 nM, respectively. On the contrary, the fully extended form, [Tyr9,Dip18]VIP(1–28), was a potent agonist with improved binding affinity (K i = 0.11 nM) and ability to stimulate cAMP (EC50 = 0.23 nM) compared with VIP (K i = 1.7 nM, EC50 = 1.12 nM). Furthermore, the specificity of this agonist to the VPAC1 receptor was high, theK i values for the VPAC2 and PAC1 receptors were 53 nM and 3,100 nM, respectively. Seven other analogs with the [Tyr9,Dip18] replacement combined with previously published VIP modifications have been synthesized and described in this work.