Elucidation of Vasoactive Intestinal Peptide Pharmacophore for VPAC₁Receptors in Human, Rat, and Guinea Pig

Abstract

Vasoactive intestinal peptide (VIP) is a neurotransmitter involved in a number of pathological and physiological processes. VIP is rapidly degraded and simplified stable analogs are needed. VIP's action was extensively studied in rat and guinea pig. However, it is largely unknown whether its pharmacophore in these species resembles human. To address this issue we investigated the VIP pharmacophore for VPAC 1 (the predominant receptor subtype in cancers and widely distributed in normal tissues) by using alanine and D-amino acid scanning. Interaction with rat, guinea pig, and human VPAC 1 was assessed using transfected Chinese hamster ovary (CHO) and PANC1 cells and cells possessing native VPAC 1 . Important species differences existed in the VIP pharmacophore. The human VPAC 1 expressed in CHO cells, which were used almost exclusively in previous studies, differed markedly from the na-

Vasoactive Intestinal Peptide (VIP) and VIP Receptors-Elucidation of Structure and Function for Therapeutic Applications

“…Alanine scanning was used to identify the amino acids in VIP that were not essential for interaction with VPACs. All of these amino acids were replaced with alanine to create [Ala [18,19]. Since the easily degradable parts were replaced with alanine, these analogs showed greater stability while maintaining the same levels of selectivity [19].…”

Vasoactive intestinal peptide–camptothecin conjugates inhibit the proliferation of breast cancer cells

“…The VIP-CPT conjugates were synthesized by coupling the CPT to the Lys 28 of (A-NL-K)VIP-L2 as described previously [19]. The product (A-NL-K)VIP-L2-CPT had >97% purity, by preparative HPLC (C 18 silica), mass spectrometry and amino acid analysis.…”

“…The product (A-NL-K)VIP-L2-CPT had >97% purity, by preparative HPLC (C 18 silica), mass spectrometry and amino acid analysis. 125 I-VIP, 125 I-(A-NL-K)VIP-L2-CPT and 125 I-Ro25-1553 (Ro) had specific activities of 2200 Ci/mmol, were prepared as previously described [19]. The radiolabeled peptides were separated using a C18 Sep-Pak (Waters Associates, Milford, MA) and fractions with the highest radioactivity were pooled, neutralized with 0.2 M Tris buffer (pH 9.5) and stored with 0.5% bovine serum albumin (w/v) at −20°C.…”

“…(A-NL-K)VIP, which is an analog of the selective VPAC 1 -R agonist, (Ala 2,8,9,11,19,24,25,27,28 )VIP, was synthesized using solid phase techniques. The VIP-CPT conjugates were synthesized by coupling the CPT to the Lys 28 of (A-NL-K)VIP-L2 as described previously [19].…”

“…(Ala 2,8,9,19,24.25.27 , Nle 17 , Lys 28 )VIP, (A-NL-K)VIP, was synthesized and Lys 28 was coupled to a linker, N-methyl-aminoethyl-glycine, L2, which formed a carbamate bond with CPT. The resulting (A-NL-K)VIP-L2-CPT was cytotoxic for MCF7 breast cancer cells, which have VPAC 1 -R, with IC 50 values of 380 and 90 nM using the MTT and clonogenic assays, respectively.…”