Ring Size of Somatostatin Analogues (ODT-8) Modulates Receptor Selectivity and Binding Affinity

Abstract

The synthesis, biological testing, and NMR studies of several analogues of H-c[Cys (3)-Phe (6)-Phe (7)-DTrp (8)-Lys (9)-Thr (10)-Phe (11)-Cys (14)]-OH (ODT-8, a pan-somatostatin analogue, 1) have been performed to assess the effect of changing the stereochemistry and the number of atoms in the disulfide bridge on binding affinity. Cysteine at positions 3 and/or 14 (somatostatin numbering) were/was substituted with d-cysteine, norcysteine, D-norcysteine, homocysteine, and/or D-homocysteine. The 3D structure analysis of selected partially selective, bioactive analogues (3, 18, 19, and 21) was carried out in dimethylsulfoxide. Interestingly and not unexpectedly, the 3D structures of these analogues comprised the pharmacophore for which the analogues had the highest binding affinities (i.e., sst 4 in all cases).

Central Injection of the Stable Somatostatin Analog ODT8-SST Induces a Somatostatin2 Receptor-Mediated Orexigenic Effect: Role of Neuropeptide Y and Opioid Signaling Pathways in Rats

“…Adult male Sprague Dawley rats (Harlan, San Diego, CA; and Taconic, Hudson, NY) weighing 280 -350 g and adult male C57BL/6 mice (23-28 g, Harlan) were group housed under controlled illumination (0600 -1800 h) and temperature (21)(22)(23) ]-Cbm-SST, MW 1137.4, compound no. 15 in (26) (Clayton Foundation Laboratories, Salk Institute, La Jolla, CA) were synthesized and purity assessed as previously described (21,(25)(26)(27).…”

“…15 in (26) (Clayton Foundation Laboratories, Salk Institute, La Jolla, CA) were synthesized and purity assessed as previously described (21,(25)(26)(27). Peptides and the NPY-Y 1 receptor antagonist, BIBP-3226 (Sigma-Aldrich, St. Louis, MO) were kept in powder form at Ϫ80 C and dissolved in pyrogen-free distilled water immediately before the experiments.…”

“…SST-14 and SST-28 interact with sst [1][2][3][4][5] receptors and display nanomolar affinity to sst 2 (16) including the variants sst 2A and sst 2B generated by alternative splicing (19). Similar to SST, des-AA 1,2,4,5,12,13 -[DTrp 8 ]-somatostatin (ODT8-SST), a long-acting agonist (20) binds to all sst receptors with nanomolar affinity (21) and therefore allows to study the effects that closely resemble those exerted by the endogenous ligand. We previously reported that ODT8-SST acts in the brain to influence digestive functions indicated by the stimulation of gastric acid secretion and emptying upon intracisternal injection in rats (22,23).…”

Ring Size in Octreotide Amide Modulates Differently Agonist versus Antagonist Binding Affinity and Selectivity

“…Boc-Ncy(Mob)-OH, Boc-D/L-Ncy(Mob)-OH, 6 Boc-Hcy(Mob)-OH and BocDHcy(Mob)-OH were synthesized in our laboratory. 7 The peptides were cleaved and fully deprotected with hydrogen fluoride. Cyclization of the cysteines/norcysteines/homocysteines was mediated by iodine in an acidic milieu.…”

“…The un-shifted amide proton resonance of Thr 10 at 7.58 ppm (from 298K to 313K) confirms that this amide proton is involved in a hydrogen bond. The side chain of Phe 7 and DTrp 8 are in the trans rotamer and that of Lys 9 is in the gauche + rotamer (Table S1). Table 1).…”